It seems they are still there and render on the front end but in the editor, they show the warning “Your site doesn’t include support for…”
@coldrealms65 I took a look at this for you.
You are correct – if you are using a non-block based Theme, then Post Author and Post Comments blocks aren’t available.
However, if you activate a block based Theme such as TT1 Blocks then you will see the blocks are available.
Looking into this in more detail it appears it was decided that those blocks require more “polish” before they are included in the version of Gutenberg that will ship with Core WordPress in 5.8.
As a result, they have been moved back into the “experimental” section which means they will only appear for Themes that activate the experimental features of the Gutenberg Plugin.
I appreciate this is likely frustrating but using Gutenberg Plugin will always expose you to changes such as these. The trade off is that you get the latest features first.
If you require greater stability I’d definitely recommend using only the features of Gutenberg that come bundled with WP Core (ie: deactivate the Plugin).
So you know, these two blocks will very likely eventually be moved back out of the experimental status and thus available again with non-block based Theme in the near future.
