I have a problem that might be a symptom of another problem, so please bear with my rambling question...
My RPi4 is running omv 6 (I can't remember if it's a clean install or if I upgraded from 5 at any point), and I have Nextcloud (together with nginx and some other images) running on docker. I can't really remember what guide I used to install and setup (dbtech's video guides mostly), but it's been working well (as far as I can tell) for months now.
Now there's an update for Nextcloud, and I would like to upgrade to it. Other containers I successfully "recreate" in portainer, which pulls the latest image. When I try to do the same with the Nextcloud app (nextcloud_app_1) I get the error "Failure pull access denied for sha256, repository does not exist or may require 'docker login': denied: requested access to the resource is denied", and the same happens with Nextcloud's database (nextcloud_db_1).
I would like to try docker-compose pull, but when I login via ssh I cannot access the drive (and the subsequent share) that Docker is installed on, despite setting file and folder permissions to allow that in as many ways as I could think of, without them giving me errors. File permissions make my head hurt, and I can't say that I understand them in any meaningful way when it comes to troubleshooting, so there might be something really simple that I'm missing. My other drives I can cd to without issues, but the one with Docker on gives me "Permission denied".
Everything looks healthy enough in the omv gui and in portainer, as far as I can see, but obviously something isn't working as it should and I can't really think of anything else to try, and googling hasn't lead me to find anything helpful.