Internal insulation for heated basement with vapor barrier or vapor retarder?

Hello, I am looking for some advice for my construction project, a well-insulated room with adequate moisture protection (it will be an aquarium room). I already have rough ideas and calculations, but I lack the practical experience to say whether it will work.

My idea is as follows: I want to insulate the room from the inside with EPS boards (preferably 6-10cm thick). External insulation is unfortunately not possible because the room is completely underground and I do not want to go through the trouble of digging everything up. With this measure, I would then achieve a U-value sufficient for me (around 0.4-0.5 for the whole room). The problem is that the room will probably not have very low humidity (I am not entirely sure yet, but I could imagine it being easily 60+%). And as is often the case with internal insulation, I will very likely have a very damp interior wall surface. To prevent this, I have been thinking a lot about how to solve this. A foil as a vapor barrier sounds good, but I will need to screw things into the wall, which will probably make maintaining adhesion and tightness difficult. OSB boards as a vapor retardant is currently my favorite option, because I could screw things to it and still have a retarding effect. However, there would still be moisture between the insulation and the wall. This is my current status, and I am stuck.

I hope this whole explanation is not too confusing and that someone might be able to give me a tip on how best to approach the problem.
Best regards, Paul

PIR or XPS - insulation boards glued to OSB boards and an inner layer of moisture-resistant gypsum boards to be pre-screwed and filled.
Mount the insulation boards on the wall with flexible tile adhesive. Flush without ventilation, the boards must lie flat over the entire surface.

EPS is not vapor-tight, PIR and XPS are. Therefore, you can drill/screw into the OSB board without problems. You can build the floor the same way, just no drywall boards, but moisture-resistant dry screed or a sealant on top to prevent swelling.

If the basement exterior wall is not well sealed from the outside, seal it first with mineral sealing slurry. 2K hybrid coatings and bitumen do not hold on the inside but come off.

First of all, thanks for the quick help. I have looked at the insulating materials and think that I will choose PIR with the aluminum coating. When I then stick these to the wall, do I have to seal between the boards with tape or something similar? And one question that I still have is, why screw the gypsum boards onto the OSB boards? Do they also serve as a vapor barrier/seal or is that purely an aesthetic aspect? Regarding the dimensioning: Does it make sense to use different thicknesses for the insulation boards, since, according to my understanding, the ceiling should be insulated best and the floor might even be negligible?!

First of all, thanks for the quick help. I looked at the insulation materials and I think I will choose PIR with the aluminum coating. If I then glue these to the wall, do I have to seal between the boards with tape or something similar? And one question that still arises for me is why screw the gypsum boards onto the OSB boards? Do they also serve as a vapor barrier or is that purely an aesthetic aspect? A little something about the dimensioning: Does it make sense to use different thicknesses for the insulation boards, since according to my understanding the ceiling should be insulated best and the floor maybe even negligible?!

There are also ready-made elements made of PIR boards with OSB boards glued on top. With OSB with tongue and groove and butt joint installation, no further sealing should be necessary if the boards fit well. For inaccurate cutting and edges, spray foam (PUR adhesive or flexible PUR from a can) is recommended to fill gaps. I mentioned gypsum plasterboards because you wrote about permanently high humidity. OSB tends to swell in such conditions. This is a basement room, right? In thermal insulation, all exterior surfaces with a temperature difference to the room in question are relevant. The exterior walls to the ground and the floor, of course, as well. Without floor insulation, you will permanently have condensation and corresponding moisture at the floor. The ceiling (if there is a heated room above) can be neglected. If there is no heated room above, you should also insulate it. For the insulation thickness, I would take approximately 60mm on all surfaces. Then lay the electrical installations on the surface; otherwise, you will have no insulation underneath and corresponding thermal bridges with potential condensation.

I have now dealt with it intensively again and made a concrete plan. However, I am still not quite satisfied with the idea of the [Feuchtraumplatten]. Would there perhaps also be the possibility of making the OSB boards completely sealed with something like paint? Spontaneously, something like epoxy resin would occur to me.