To add to that.. If OP owns a domain, they could issue an SSL cert for a subsain, like lab.example.com and point the A record to the (hopefully static) IP if the router, and port forward 443 to pihole
Most of the docker services use mounted folders/files, which I usually store in the users home folder /home/username/Docker/servicename.
Now, my personal habit of choice is to have user folders on a separate drive and mount them into /home/username. Additionally, one can also mount /var/lib/docker this way. I also spin up all of these services with portainer. The benefit is, if the system breaks, I don't care that much, since everything is on a separate drive. In case of needing to re-setup everything again, I just spin up portainer again which does the rest.
However, this is not a backup, which should be done separately in one way or the other. But it's for sure safer than putting all the trust into one drive/sdcard etc.
I'm not familiar with mint, but maybe you can see whether you can easily downgrade to the previous version you had. And hold off on the updates until a fix is published for the broken stuff.
But before that, take a look at the mint communities and see whether it's a known issue and whether there is a manual intervention needed to fix it. Something like "newest update broke some proton games", etc.
Can you pinpoint what you did to your system before? Did you do a system update? Did you move game files around? Did you add any repositories trying to install something that also updated other dependencies, or alike?
Not familiar with owncloud.
But can't you set something like "http://127.0.0.1" as domain?