Hey Aslad, welcome to the forums.
I’ve had struggles with the interior stairs for cuboid rooms too since the update, they used to snap to the inside of any cuboid but now they only seem to snap to two cuboids with a cuboid floor and will not snap to cuboid that have doors on them. Hope this helps.
I’ve learned sometimes you need to build unnecessary cuboids and floors just to get the stairs where you want it, you can then delete the unneeded cuboids and floors and the stairs will remain so long as the cuboid room it is in is not deleted. Then you can place what you want at the foot and head of the stairs.
This is only way I’ve managed to place them without having it connect to a false floor.
For example I used to place cuboids in a diagnol fashion with stairs going up, no false floors needed as each cuboid had its own original floor. Stairs no longer snap to the original floors of a cuboid, only the false floors now. So to achieve diagnol cuboid stairs you need to trick the stairs to do so using the above tip. It’s extra work but you can figure out a few hacks and tricks by messing around with things like that.