Hi @angus,
Another update: I installed the Query Monitor plugin (in WP)(see output, below).
Using cURL at my local computer, I also get a 403 so it seems to me this is an upstream issue my site ans WP Discourse. Probably Cloudflare but I don’t want to remove Cloudflare yet. See below.
Another apology for my slowness. I have received a notice from my hosting service that my site is being migrated to another server and there will be some changes, including a change of IP. So I need to delay further work on this problem. May I call on you again when the dust settles?
EDIT: Solved! Perhaps a bug at /admin/site_settings/category/security -> allowed crawler user agents.
It appears that any entry in the allow UA text actually causes a block of all, even a curl command line from my local computer. Resetting the text to empty immediately results in WP Discourse " You are connected to Discourse!