Not able to click below block to create a new block in gutenberg

so it works with AO disabled and does not work when AO is enabled? or is the difference more subtle? ??

When AO is active then I can not add blocks by clicking below the current block. (AO is the only plugin except Gutenberg which is active.)
When AO is disabled then I can add blocks by clicking below the current block.
As there are a few different issues on the Gutenberg repo I am thinking this has a much higher impact than just when AO is active. As it might have an impact with plugins that add metaboxes in general.

so does disabling the “Enable configuration per post/ page?” option near the bottom of Settings -> Autoptimize -> JS, CSS & HTML “fix” the problem?

Settings -> Autoptimize. Disable “Enable configuration per post/ page?”
Actually does fix the problem!

So this is a metabox issue then. Interesting! I will bring this back to the Gutenberg issue I posted in.

interesting indeed! if there are other plugins with metaboxes that also trigger this bug, then indeed this is likely something to be fixed on gutenberg side.

I just tested with installing and activating Yoast SEO plugin which also adds a metabox to the gutenberg screen. The problem also showed up there. So this is a Gutenberg issue.
I will close this issue and mark it as solved.

seems to be (at least related to) https://github.com/WordPress/gutenberg/issues/63882 ?

I went ahead and reopened the issue 63882. We will see what others say.

It got the reaction that a fix is coming. So that is very good news!