I Can't Get Ghost 6 ActivityPub To Work When Self-Hosting

I love Ghost, but I simply can’t get their ActivityPub functionality to work in a self-hosted configuration. I have done extensive testing: using the New Install (i.e., Docker) option on both Digital Ocean and Vultr with this domain and fresh domain using self-hosted and Ghost’s own ActivityPub infrastructure using a Ghost admin domain at site.tld/ghost and admin.site.tld proxying and not proxying using Cloudflare Nothing works. When using Ghost’s infrastructure, I receive Policy Violation errors. When I use my server’s own ActivityPub service at :8080 I get HTTP 403 errors. It’s a little disappointing. However, when self-hosting, the native analytics with TinyBird worked as advertised and were really well presented, though not as in-depth as Plausible. When not self-hosting I tried one of the fresh domains above with Ghost(Pro) and the ActivityPub functionality worked. It was marvellous. I’m really hoping these issues are just early 6.0 bugs for self-hosters. Some credit to Cathy Sarisky for helping the community.