Description

I can't edit my site anymore. Loading https://mysite/wp-admin/themes.php?page=gutenberg-edit-site&postType=wp_template&postId=mytheme/index is horribly slow to load.
Header & Footer are loading, then middle of the website block (contains a query loop).
I can't even disable Gutenberg with WP 5.9.3 since I used stuff not available there (to avoid a bug) and my site crashes without it.
I feel stuck & it's hard to help you to debug.
If I wait several minutes things start to load, but "it depends", most of the time safari crash "this page used too much memory shah blah blah" & chrome is having a hard time to.

Some times, after several minutes, I can use the editor. Sometimes it's probably consuming too much memory and crash.

FYI, I have made a time from the FSE with a very simple theme.json when I started. Minimal functions.php (a few lines).

Step-by-step reproduction instructions

I just need to open the FSE UI on a page with multiple menu, a single query loop with 10 posts with title, categories, date & thumbnail.

Screenshots, screen recording, code snippet

Note that in the video, you can notice that the safari timeline doesn't start immediately, but at 1:50 ! 😱
During this 2 minutes, my computer does nothing. I have MacBook Pro M1 Pro 16, so perf is not an issue there (but Safari consume a CPU at 100%) !

Environment info

• Wordpress 5.9.3
• Gutenberg 13.0.0
• Safari Version 15.4 (17613.1.17.1.13) or Chrome Version 100.0.4896.88 (Official Build) (arm64)

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes