Uneven floors and furniture leaning forward

Hello, I am renting an apartment for some time and got a chance to get a nice used 2mx2m wardrobe for free, I started taking it together today and noticed when it is put against the wall, it is leaning forwards more than I feel comfortable.
I checked, basically, all the floor is sagging and the lowest point is the middle of the room.

as I am not able to put it right against the wall at the lowest part it is about 4 cm away and on the upper part 2m higher it is 10 cm away... 6cm over 2 meters seems crazy.

Also, the wardrobe does not really have legs and it is almost right against the floor.

1) So how safe, in general, is to have it leaning forwards? I understand it could be screwed to the wall, but at the top it already y is 10cm what seems crazy and ugly
2) Could I put something below the front part to make it lean back? Issue wardrobe, in general, is very top-heavy and I have not even attached doors yet...
3) Could this actually be a more serious issue with the house/room itself? I did check all the walls with level and none of there were straight :D Seems the whole house is leaning to one side a bit (furniture however is not leaning to the same side, but to the middle of the room instead)

It is not really my apartment or my house, so I don't care too much about long time effects, but still plan is to stay here for some more time still (hopefully the virus will bring some real estate prices down)