Can not place stairs unless already I'm already in build mode (R Keybind)

I just switched to kbm and I am having this issue wth the J key as well

Just experienced this myself, it is caused due to another R keybind taking precedence to the build keybind.

Remove all ‘R’ keybinds

Restart the game (must)

Bind R to the build piece you want

Should work for any other key.