When i for example put 1728 shulker boxes in a chest and there is a hopper connected the hopper will now take 5 stacks of shulkers instead of just 5 is there any fix for this?

It's a new vanilla feature of stacking shulkers -- they will stack everywhere now when they are set to 64, even in hoppers.

Would it be possible to add a feature that reverts this new vanilla behaviour? The new stacking boxes can break contraptions.

it sucks and breaks so many contraptions

This issue seems to be a duplicate of #1916.

It's a new vanilla feature of stacking shulkers -- they will stack everywhere now when they are set to 64, even in hoppers.

Vanilla?

It's a new vanilla feature of stacking shulkers -- they will stack everywhere now when they are set to 64, even in hoppers.

Vanilla?

If you set the "MAX_STACK_COUNT" data component, that's what will happen. A Mod isn't even required to get stackable shulker boxes under 1.20.6+