When trying to build an elevator with the happy ghast, pushing it into a minecart and putting that minecart into a bubble elevator will transport the player down perfectly when having a magma block at the bottom of the elevator. Now if you put a soul sand block at the bottom of the elevator you will just clip through the ghast and won’t be transported upwards. This works perfectly fine on bedrock and is crucial to building a happy ghast elevator.
Environment
1.21.7, Vanilla, Java edition
Can confirm.