@jeremycherfas I've set up a ClassicPress site and the Indieweb plugins all worked. I detailed it here: cyberzettel.com/successfu...
The major hitch was from my host which runs an auto-update robot for all Wordpress installs, for security purposes, which kept reverting my ClassicPress site back to Wordpress every half hour. I had to get them to turn that off for my ClassicPress install.

@bradenslen Thanks. I've done it for one of my own sites too, absolutely painless. This is a bigger site that was failing a PHP upgrade to 8.2. I knew this day would come, and as I have no need for the bells and whistles of WP these days, time to make the change.