So sorry for the delay here @angus. Can we try and add tag support to ActivityPub without tag custom fields?
I know it’s not consistent with the data model we’re currently using there for categories, but it’s our preferred approach. Adding custom fields support for tags in core means we’d open the door to full support for them in core, I know your PR doesn’t add this, but it will nudge the next developer to push the door slightly more open.