Yeah, it's not you, it's a bug. I recreated the same situation OP showed in their images and used the same stairs in the same configuration. If you place those stairs on any floor above ground level, they work just fine. If you swing around the lower 4 steps 180° to the other side you can place the stairs inside the room on ground level just fine as well. If you then want to rotate the lower 4 steps back to OP's original configuration, the stair placement becomes impossible again. Feel free to file a bug report and maybe it'll get fixed somewhere in May... 2024 ;).
