What app is this about, and its version: NextCloud, v26.0.2~ynh2 What YunoHost version are you running: 12.1.27 What type of hardware are you using: VPS bought online
Describe your issue
I was trying to upgrade my NextCloud server after a long gap. I updated all the NextCloud apps to their latest version first (within the NextCloud admin) before proceeding with upgrading NextCloud.
Unfortunately, the upgrade failed saying that the app “Mail” could not be installed due to being incompatible with this version of the server.
I already solved this, but posted here in case it helps someone else! My solution was to uninstall the “Mail” app from NextCloud, perform the upgrade, and then reinstall the “Mail” app.
I think this is because the NextCloud upgrade has to go through each version: first 26 to 27, then 27 to 28, and so on until the latest (31). The Mail app supports NexCloud 31, but maybe it dropped support for some of the intermediate versions along the way.