I think you must misunderstand the purpose of Dolphin since it is nothing like Tonido. A good analogy for Dolphin is Windows File Explorer. This particular docker implementation of it is just giving you a Linux desktop in a browser with the Dolphin file manager already launched.
Yeah, sorry my end goal was always just something to manage my files without managing them from my other systems, not necessarily to have access to the files remotely like with Tonido. I still like being able to manage files while I'm away, but would rather not have it open to the world. With that in mind, is there a way to lock it down?
Best option is vpn, second best is to use a reverse proxy like nginx. With reverse proxy, you can set a password through .htpasswd
For vpn, check out the openvpn server dockers
For nginx, you can use either the nginx docker or the letsencrypt one I have, which sets up a free 3rd party SSL certificate with nginx
Many new routers have VPN built-in. I use the built-in VPN on my ASUS router, and I also use Teamviewer to remote control computers on my home network.