We have an EOL Nextcloud 27 with similarly outdated plugins. We tried many times and cannot upgrade. The system runs on a cloud cluster. We duplicated the production environment to test-run the upgrade process, we tried many times and it always fails.
At this point we are looking for a professional with deep knowledge of Nextcloud, Linux and cloud, who can solve this issue because we are out of ideas and out of time.
Contact me here or at: carlaaniach.maritime474@passinbox.com
Unfortunately, I can’t help you directly. But as a tip, I would start by uninstalling all the apps you don’t really need (on the test-upgrading-system). If the pressure is high enough, not much more than the standard apps should remain. If the upgrade then works, you can try reinstalling the apps. Please note that any existing data for these apps will be lost.
if no one gets in touch, you are welcome to post the errors of the update here. Perhaps we can provide a little support.