V2 volumes do not support live upgrades between Longhorn v1.12 patch releases and must be detached before upgrading. Support is planned when upgrading from a Longhorn v1.12 release to a Longhorn v1.13 release.

Is it correctly understood, that if I create a V2 volume and when in a few months I need to upgrade from 1.12.0 to 1.12.1, I would need to delete my app deployment before the upgrade?

I think it just means you can't do it without scaling down the workload and having downtime. Don't think you have to delete it

Ok, same outcome though, downtime :)