I’m still unclear how you updated the Calendar app and then ended up at the Server update screen. Can you describe precisely how you upgraded Calendar? Are you using something like Watchtower that might have upgraded your Nextcloud image/container as well?
You basically have two mysteries here:
- How did upgrading an app lead to your entire server updating?
- Why are you stuck with an unfinished update?
We can suggest some commands that might work, but they won’t solve the mystery and I don’t like telling people to blindly finish an upgrade that wasn’t triggered to start with. 
Please check your Nextcloud Docker container start-up logs. That’s where the upgrade process runs for most Docker images, including the LSIO one you’re using. (In native docker the command would be something like docker compose {container_name} logs at the command line but I’m not sure how much OMV abstracts you away from the native Docker commands).
Also, please check your nextcloud.log for additional clues. There may be something else going on here.
Add’l Refs: