Howard Miller

Have they checked that the filters are set to "no filter" on the submissions page. 90% of the time, that's the problem when "I can't see any submissions" is reported.

curl error 28 normally indicates a timeout.

Moodle is checking for available updates but is unable to do so. Probably something like it getting blocked by a firewall. Or simply no internet access from your Moodle location.

You can enrol users using the flat file enrolment method - see Flat_file.

Authentication, automatically, from a flat file doesn't make any sense to me. It's something you only do once. If you want to automate your user authentication then where is the user data originating? It would make more sense (to me) to use one of the existing authentication plugins (e.g. external database) or script something using Moosh's user-create command (https://moosh-online.com/commands/).

But the devil lies in the detail of exactly what you are trying to do.

This is nothing to do with adding plugins. Or not directly at least. I expect that someone has upgraded PHP on your server without telling you.

You have two choices... you downgrade PHP back down to 8.1 or you upgrade Moodle. Moodle 4.4 is just out but 4.3 also supports PHP 8.2.

I see what you did there