How to I manage to remove just this part of the floor?
I tried to close this square like if it was a room, then clicked on "remove floor", but then when I remove the wall, the floor comes back. https://i.imgur.com/Gj4vJVS.png
Put your full wall back, then click inside the little room and push or pull the wall all the way to the back wall, then you get rid of wall and floor. :)