So, a dev upgraded php to php8.2 (in fact the whole server was upgraded) and broke the Osticket installation.
My fix was install 1.18 and then swap databases, this then prompted a few database updates and I could log in. (looked like the devs had expected someone to do that!)
there was a imap for php8.2 issue, that I fixed with a quick php.ini edit and a "sudo apt-get install php8.2-imap"
Unfortunately it is still not fetching mail (using AUTO CRON), the IMAP server is on the same machine.
Any pointers?