If you installed Nextcloud from a snap, you can list it with a command like the following:
user@host:~# sudo snap list Name Version Rev Tracking Publisher Notes core 16-2.38 6673 stable canonical✓ core nextcloud 15.0.7snap1 12753 stable nextcloud✓ -
…since “stable” is seen in the “Tracking” column above (in the “nextcloud” line), this tells you that the snap will indeed auto-upgrade itself, once a new major version release of snap for Nextcloud gets published in the “stable” channel (and I use the word “channel” here in the snap sense of that word, as in, a “snap channel”, as known to the snap command).
For example, what if you’re contented with ver. 15 right now, and aren’t feeling ready yet to automatically upgrade to 16 (once it’s published as a “stable” snap)? Here’s how you can tell snap “just stay on version 15 until further notice, please”:
user@host:~# sudo snap switch --channel=15 nextcloud
…should yield the output:
"nextcloud" switched to the "15/stable" channel
Now list the snaps again with “sudo snap list”, and you’ll see this instead:
Name Version Rev Tracking Publisher Notes core 16-2.38 6673 stable canonical✓ core nextcloud 15.0.7snap1 12753 15 nextcloud✓ -
Note the “15” under “Tracking” now! Once you are ready to unleash Nextcloud 16 (after it got published in the “stable” channel, at some future time, say a few months from now), you can just set the channel back to “stable” again:
user@host:~# sudo snap switch --channel=stable nextcloud
…which will be tantamount to telling snap “yes, I want 16 now (granted that’s the currently “stable” version published as a snap)”.
Note: You can check which is the currently “stable” version here.