One of WordPress’ block editor’s “nastiest” quirks is how it deals with “classic” meta boxes, including the Custom Fields panel.
It’s why in my ActivityPub add-on plugin, I had to “delay” federation to a later hook (than transition_post_status [and use a static variable to temporarily store the new and old post statuses], but only when rather specific conditions are met).
Anyhoo, I literally wrote about this countless times, and still occasionally get it wrong.
As for IndieBlocks, I have added a “dedicated” Webmention “sidebar,” but it’ll only show if webmentions are scheduled (or were sent previously).
The Location panel, when enabled, is still added to the main sidebar. Just like Share on Mastodon’s. Had to do with actually (and automatically) triggering the browsers navigator.geolocation’s functions, too, I believe.
Would’ve been cool to have a “proper” IndieBlocks sidebar (and even add Share on Mastodon’s panel to it, and Share on Pixelfed’s, something I wanted to use Slot and Fill for). But this is probably better, for now.
Jan Boddez