When I union some parts it’s apply a wierd collision to the union what blocks the player from walking trough and even clicking on surface uis covered by unions
Idk if this a bug or there simple solution to solve I already tried to use different collision group thingys but none of them seem to work
Did you try the CollisionFidelity?
Search the forums first please.
There are so many posts about this topic.
Basically if you Negate a smaller percentage hole out of a large Part or Union the actual shape of the physical hole is different from the visual shape.
Try changing the CollisionFidelity to PreciseConvexDecomposition as @SomeFedoraGuy said to see if it helps.
If it doesn’t read the other posts you found in the Search above for more help.