What problem does this address?

Please, think about tailor-made themes that are coded from design to WordPress.

We need to control block settings being to able to turn off user's modifications like Layout and Width panels (and other "new features"). There is no way to turn them off and they are causing many headaches - clients call you "why it doesn't work in our theme", but the designer hasn't prepared those options. And the reason why this happens is that the new WordPress is released. I mean - I want to use the latest release, but I don't want to use certain features that are not ready in design.

I haven't found a way to do it.

Looks like it's related to #19796 that was never solved.

What is your proposed solution?

Add theme.json settings that will easily allow setting panels off - in settings for all blocks, in blocks for separate blocks. I believe that theme.json should be the place for all edits. That would enable to quickly disable unwanted features and at the same time keep latest WP version.