@smilebasti The /home/yellowtent/appsdata is the location of apps. This size seems to roughly match the nextcloud size. As for docker, you should not use du tools inside docker's image directories since they are overlays and the du tool is not smart enough to figure out the size correctly. Try docker system df to get a better idea about the actual size docker uses (this is what is reported in the graph as ~5GB). The volumes also link into appsdata so they might be double counted the du tools.
To take a wild guess, maybe you were backing up to the file system for some time before you moved to NAS via SMB? If this was the case, then you should remove the old backups manually from /var/backups. You can just safely nuke all the timestamped directories and the snapshot directory inside it.
@randyisscott I'm not entirely sure if the article I saw on https://www.proxies.com/ipv6 is attending to my question. I don't think I need all the additional trusted domains and trusted proxies stated there. Trusted domains are meant to tell nextcloud to allow access when you access it at cloudxxx or by IP address. They also have a duplicate in there, probably need to remove that. Trusted proxies I believe should only list the IP address of the proxy server, nothing else. I'm not sure if that affects the redirect loop but I would start there.