Final Cut Pro 10.6.7 Extreme lag issues

Hey, I recently updated to 10.6.7 from 10.6.5 (because I heard that 10.6.6 was little bit laggy) so I tried updating it straight to 10.6.7, I thought that Apple has fixed issues which was in 10.6.6 version. So after updating my library and projects to the newest version it completely destroyed them. It's impossible to edit smoothly like it was on 10.6.5 and it keeps crashing, freezing and randomly shut downs.

Is there any way to convert my "Library" to the older version of FCP?

Also some users reported that they get message "Editing 4k footage and higher is not recommended on this device even if they have newest and highest M2 MAX chip on it"