I’ve been having this issue for a while, and recently its been getting worse and worse. Every time I try to scroll in the designer I get extreme lag and jittery scrolling, However I have no issues or lag with editing actual objects on the page. It’s only a scrolling issue.
I’m using Safari version 15.5 (17613.2.7.1.8) on Monterey 12.4 on a late 2017 MacBook Pro
Just encountered this…when few minutes ago Designer was scrolling fine… I had a hunch…I had loads of tabs open in FFox…closed a few down… problem solved… I guess FFox was taking up too much working memory… See if it works for you