I tried to edit Feature request: per-category reactions, but got
… which seems like a bug but is is also very exciting. What’s going on?
AI-generated summary
Users are experiencing an error when trying to edit a post with the ActivityPub plugin enabled. The error message states that editing an ActivityPub note after publication is not currently supported. pfaffman confirmed that this is a known limitation, but noted that it is on the roadmap to be changed. angus mentioned that a Pull Request (PR #14) is underway to lift this limitation. In the meantime, users will need to be patient while the ActivityPub support is tested and rolled out. Note: The plugin seems to be running on meta.discourse.org, which is why users are encountering this issue.
It’s a known limitation.
I think if you read on that changing that is on the roadmap.
Oh, but maybe the surprise is that this plugin seems to be running here!
EDIT: Sorry it took so long to understand that was what you meant! I had just read the whole ActivityPub topic, so I was quite impressed that I knew anything about it.
As @pfaffman noted, I believe this is currently a limitation of having the Contribute > Feature category linked up to the ActivityPub plugin. Hopefully it won’t be too inconvenient, though it’s caught me out a couple of times. 
This limitation will be lifted once this PR is merged and deployed. Thanks for your patience while we test and roll out ActivityPub support (it’s quite complex).