Howard Miller

"The command to run composer presumes your Moodle folder is owned by www-data"

What about sites that do not run the web server with that user. Do you possibly mean 'not root'? Unsure...

"After the upgrade, plugins previously installed will still be in their original locations above the /public folder."

This statement doesn't make much sense to me. If you upgrade from previous versions then you would completely replace the code with the new version. Optional plugins all need to be re-added to the code. This can, of course, be done in several different ways. But I'm struggling to see a scenarion where they would *still* be anywhere...

Composer is - to be fair - very well known in PHP circles. However, as an end user it's probably not something you should be expected to be aware of.

"P.S. I don't think the idea of Upgrading to 5.1? Read this first was not to collect every case of Moodle 5.1 failing to collect here. "

Well, I suppose we're all learning stuff. There may be a more helpful pinned post by Tuesday

This page - https://docs.moodle.org/500/en/Configuring_the_Router

...says "Configuration of the Moodle Router will be compulsory from Moodle 5.1 onwards". Which (someone correct me if I'm wrong) is at odds with the Upgrade page that doesn't mention it at all.

Sigh