The copy protections on Blu rays are exceptionally annoying, to the extent where there is really only one closed source software – MakeMKV – that can work around them.
Not quite, RedFox formerly SlySoft (RIP) used to market their own Blu-ray ripper and it worked quite well. What it used to do is on-the-fly decryption so you'd run it in the background and could use any other software to read the decrypted Blu-ray (e.g. using Handbrake or whatever). It did also have an option to just rip to a file IIRC. Unfortunately they randomly disappeared so their software is pretty much done. (some background on wikipedia https://en.wikipedia.org/wiki/RedFox)
That aside they always a competitor, DVDFab, that still exists today. Their Passkey software is the rough equivalent of what the old RedFox/SlySoft software used to do but they also sell a standalone Blu-ray ripper if that's more your thing (see https://www.dvdfab.cn/).
But yeah, in some ways you're stuck with MakeMKV, DVDFab, and maybe some others (?).
I'd have to dig it out but I actually bought a Blu-ray drive a while back that was on the list of drives compatible with these rippers but honestly it's been a few years since I've tried using it. Most times someone else already ripped a Blu-ray I'd be interested in.
Speaking of - If anyone knows offhand, how do people do this stuff on Linux? Does the Linux version of MakeMKV work well for this and/or are there other tools (?)
Just to be sure, did you already test that the port is actually open and forwarded? e.g. with your torrent client running browse to a port test website like https://canyouseeme.org/ , https://www.yougetsignal.com/tools/open-ports/ , etc. put in your torrent client's incoming port and check if the website can "see" your open port at your torrent client.
And the ISP (or router) itself isn't doing anything weird to block torrents, right? In your torrent client if you click any working public torrent, click on the Trackers tab, you should see DHT as working along with whatever open trackers are on the public torrent. In other words you won't see anything like "waiting" something (I forget the exact message you'll see when DHT is being blocked but it'll definitely not be working).
EDIT: Also if it's a new ISP with new router it might have firewall rules set up that are slowing things down, something to check.