I'm thinking of gluing wooden panel to drywall ceiling (ceiling, not wall). I'm wondering that's the maximum weight per square meter that my ceiling will be able to hold.

>>2925153 (OP)
That depends a lot on the ceiling material. The right way of doing this is remove the ceiling, add wood strips to level the ceiling and then fix the boards to that. Quick and dirty would be to screw the wood strips through the ceiling into whatever is above the ceiling.
But the main question is: why would you want to put flooring on your ceiling?

>>2925153 (OP)
If this is to get some kind of look for the room have you considered using wallpaper ?

>>2925231
Okay now I think the best course of action will be to paint an EPS panel and glue that, because they're lightweight:

https://www.amazon.de/Decosa-Creative-Panel-Wood-Effect/dp/B01MZB1G0C?ref_=ast_sto_dp&th=1]

the problems are:
1. it'll require work
2. I'm a shit painter

but eh. I want my room to look more cozy, therefore more brown color needed (not poop)

>glue
why not use small nails or screws?

Gonna make the room super dark. White ceilings reflect light.
Enjoy your dungeon and living in fear of falling wood.

>>2925462
Real medieval castle experience. I'm sure someone would pay for that.

>>2925420
Fastening to the joists would make max load too simple to solve for. This way we can solve for 5/8 drywall tear-out and plaster.