I’m new to this program so I don’t know if what I was even trying to do is a solution to my problem, but I wanted the collision to only apply to the middle of the object so I get rid of the gaps, though it was greyed out.
The “Apply Collision(s) to Selected Tiles” action is for assigning the selected collision shapes to all selected tiles. It’s a bit of a workaround because it is at the moment not possible to edit the collision shapes of multiple tiles at once.
I don’t really understand what you’re trying to achieve, but I don’t think this is the action you are looking for.
If you want to close the gaps between the visible portions of your tiles, then you should set your map’s tile size to be 1-2px smaller, so that the tiles overlap. Depending on how you handle the collision, that should also remove the gaps between the colliders if they cover only the solid portions of the tiles.