Error while updating from 19.0.4 to 20.0.1

Was updating from 19.0.4 to 20.0.1 using the updater (which in previous updates has worked well for me)

Updater ran ok and I chose to Not keep maintenance mode active. Then during the update step got the message

Update to 20.0.1 for a couple of minutes and then:

Detailed logs say
‘An error occured’

Now stuck in maintenance mode

What to do?

So I updated maintenance mode to ‘false’ and can now access Nextcloud and its obviously a new version. I’ve moved around a bit and at a high level things seem to function.

However, how do I know if the update was completely successful and whether I can proceed with confidence that everything is working as it should?

did you also looked into the nextcloud error-log and php error-log?

Similar thread

Now I received an email with the following cron job output :

Nextcloud or one of the apps require upgrade - only a limited number of commands are available You may use your browser or the occ upgrade command to do the upgrade

Command “preview:pre-generate” is not defined.

Did you mean one of these?
migrations:generate
preview:repair

I also then subsequently received additional cron job output :
Command “preview:pre-generate” is not defined.

Did you mean one of these?
migrations:generate
notification:generate
preview:repair

Looks like the app Preview Generator was not enabled. I have now enabled it. I have version 2.1.0 of Preview generator. I see version 3.1.0 which seems required for Nextcloud 20 but it doesn’t seem to be flagged to update. How do I get the latest 3.1.0 version of Preview Generator ?