Hi there Mohamad, and Welcome to the forum!

I am happy to be here for the first time after finding the way to this forum after I got tired of other sites.
Other sites are strange math equations to create a mixing and mastering room and not understand something.
The math certainly can be very confusing, and doesn't really help to design a studio for people who don't like math. That's why I try to keep the explanations simple here on the forum, with as little math as possible.... and sometimes, a lot of words instead!

Some of my posts get to be quite long...
Sometimes mathematical people tend to forget that all those convoluted equations are just a way of describing how the real world actually works, but it an also be described in words and pictures! Everyone understands words and pictures, but not everyone wants to understand the math.
I was renting an isolated office and it was damaged after the explosion and lost everything
Wow! I'm so sorry to hear that! I saw many videos of that explosion, and it was huge. Immense destruction. I've also seen photos of the extensive damage to many, many buildings. So much destruction, so many dead, and so many injured. Just shocking.
It must also have been devastating for you to lose your studio and your livelihood in an instant like that. I can't even imagine what that would be like.
Fortunately you have another room that you can use, and it is a decent size, with a ceiling that is not too low: that can be a pretty good room for mixing/mastering. Nice!
walls of reinforced concrete on all sides with a thickness of 25 cm for each wall, and three of these walls have infinite thicknesses as they are under the basis of the building, or it can be said that it is under the ground and the ceiling is made of concrete,
That's excellent! You will have extremely good isolation like that, except perhaps to the sunroom above you, but your isolation from the outside world will be really, really good.
My room sizes:
Length: 685cm
Width: 358cm
Height: 280.

That's nearly 25 m2 (about 260 ft2) floor area, and 69 m3 (2,400 ft3) room volume, so that is larger than the minimum recommended area (20m2), and with decent air volume. With proper layout and treatment, that room can definitely be a great mixing AND mastering room. Mastering rooms need to be bigger and more accurate than ordinary mixing rooms, but you have the size and volume to achieve that. You are in a good position here.
Concrete floor is not tiled yet , I may lose a few centimeters in height after tiling.
Tiling is great for a studio floor, but you can keep a little more headroom by just using laminate flooring or vinyl flooring. Good laminate flooring on an acoustic underlay only takes up about 13mm thickness, and makes for a good studio floor. Vinyl flooring can even be a bit less than that. In both cases, there are some very nice finishes available today that look really nice. You just need to have a very level, flat, smooth surface for both of those: for tiles, it isn't so necessary since you will put down a bed of tile adhesive that can help compensate for minor unevenness. All three options are good. One other one is to polish the concrete, if it is in good condition, and perhaps stain it. That can also look very nice. All of those are good acoustically too.
The room definitely needs ventilation,
Where would be the best place to bring in the ventilation ducts? I imagine that they will have to come down through the ceiling, from the sunroom, since the four walls are all underground. Maybe you could mark on your diagram the possible places where the ventilation ducts could come through? Also, how thick is that concrete ceiling? You will need two ducts: one for bringing in fresh air, and the other for exhausting the stale air. You will need to calculate the sizes of those ducts (sorry! That involves a bit of math....

).
You will also need an air conditioner, and you have two options here: 1) a ductless mini-split mounted on the wall inside the room, or 2) a ducted mini-split mounted outside of the room, perhaps in the sunroom itself, if there is space for that. The advantage of that #2 option, is that it is much quieter: Even though ductless mini-split units are quiet these days, you will still hear them in a very quiet room, such as yours, and that might be annoying if you are trying to concentrate on a complicated mastering issue. For example, if you are working on a very soft, "breathy" vocal track, the sound of that mini-split fan and air movement might distract you or confuse you. It's not usually a problem for most situations, but for a precision mastering studio it could be an issue. A ducted mini-split outside if the room is totally silent: you won't hear it at all, if the system is well designed. There's some ore information about studio ventilation here:
why your studio needs proper HVAC. and even more here:
Studio HVAC: All about mini-split systems, HRV's and ERV's. the room sizes do not match the golden ratio or the Bolt area, I plan to make its length about 5 meters to match minimum room modes
To be honest, I would suggest not doing that: It would make the room 1.85m shorter, reducing the area to just 17.9 m2, and the room volume would come down to 50m3. That area is now SMALLER than the minimum recommended floor area for a critical listening room (20m2), and you lose nearly 30% of your room volume (about 28%, to be more accurate). Yes, you will get a better ratio, but that isn't really the biggest or most important factor to take into account. I'm not sure if you have seen this article that I wrote about that:
viewtopic.php?f=16&t=557 You might find that useful.
The largest size that gets you a ratio within the bolt area, is Length=6.15 m, Width=3.58 m, Height=2.56 m, and that reduces your floor area to 22m2, volume to 56m3... But the Bonello graph then is actually less smooth than for the original size! And there is still an issue with one of the three fundamental ratios: the room is too long for the height and width. You have to get the length down to 5.81 before you can meet that criteria, which reduces the area to 20m2, and the volume to 53m3. Acceptable, on the borderline, but the Bonello graph is still not any smoother than for the original full size room. The only way to get good numbers all around, is by making the room 4m wide! But that's not possible, of course.
The other issue here, is that if you cut off 1m from the back of the room, you also cut off the doorway! So you would then have to access the room through the UPS battery storage area, through a door in the middle of the rear wall. That adds extra doors, and makes access tot the studio a bit harder, plus it puts a door in a location where it would b better to have treatment.
So, here's what I would suggest: Keep the room the full size, flush mount your speakers in "soffits" in the front corners of the room, then build a "closet! in between the soffits for your UPS batteries and other storage. If necessary, you could even make the soffits deeper than the need to be acoustically to gain more storage space. That also means your door remains on the side, 1m from the rear wall, which gives you plenty of space for the rear wall treatment, which is critical to good room performance.
The issue with "room ratios" is this: For a small room, ALL of the ratios are "bad", in the sense that you just don't have enough modes in the low end! The ONLY way to solve that, is to make the room very large... and of course, that isn't possible for the vast majority of home studios, and even most professional high-end studios. So, you will ALWAYS have modal issues on ANY small room: the only question is, will they just be "bad" or will they be "terrible"? And in either case, the solution is just to treat them! Any small room is going to need a lot of treatment, but the smaller it is, the more treatment it needs. So, keep it as big as possible, and use all the space you can spare for treatment.
It's that simple.
But a lot of people misunderstand the importance of room ratios, because you see so much about them, all over the internet. In reality, there are not that important! Yes, if your room happens to have a good ratio, then that's nice. Only if you have a terrible ratio, such as a perfect cube, only then does it make sense to see if you can improve that by moving walls of the ceiling... For most home studios, where the room already exists and is a fixed size, there's no need to try to chase after a "perfect" ratio... because there is no such thing!
So that would be my recommendation for your room: keep it full size, flush-mount your speakers (which is ALWAYS a good idea, in any studio!), then build your storage space into the soffits. If you need still more storage space, it would be possible to incorporate something into the rear wall as well.
excuse me, I am doing my best to draw it and also my English is not perfect.
The drawing is fine, and your English is great!

- Stuart -