In 12.1, when trying to move clients into their correct group manually, in the window that comes up, all groups are not collapsed as seen below:

In 11.x, the groups were collapsed by default allowing you to click the + button when needed.

It is painfully difficult to navigate through in 12.1 when you have a large amount of groups to sift through.

I propose it go back to the old setup like in 11.x or at least add a button that can be clicked to "Collapse All"