So I checked, and there are no "official" current LineageOS builds for any Nokia phones (unless I'm missing something on https://download.lineageos.org)
There don't seem to be any builds anywhere for the 4.1 (is it an uncommon phone?)
For argument's sake, let's say you bought the 6.1, now your option is to download an "unofficial" ROM from some pseudo-anonymous person with an anime avatar from XDA, hosted on whatever free file hosting they can find today.
Don't get me wrong, I used Lineage when it was called Cyanogenmod, and it saved one phone from landfill which is great. But I'm older now, and I need my phone to work and work well - I really don't have time for problems like https://forum.xda-developers.com/showpost.php?s=76595163ac85.... For some people, that's worth the money.
Similarly, I've pretty much given up on LineageOS ever getting the Nexus 5X to the 16.0 version. Their list of supported phones looks decent, but when you realize they can't keep even those phones up to date the project starts to look like a failure.
I'm hoping to find an alternative for friends and family who still have the 5X - it's been dropped from Google's security updates for a while, because their support ends abysmally quickly.
You hit the 5X jackpot - up to a certain manufacturing date, those phones were notorious for bootlooping and never working again.
More on topic, the LineageOS support requires a volunteer maintaining a buildable tree for the phone, and testing will require the hardware itself. I'm not sure how much CI/CD helps here.
You're right: of the four 5X phones owned by close friends or family, only 1 bootlooped (and one was stolen). It would be great to have continued support for the remaining phones, but planned obsolescence is too strong.
The Nexus 5X supposedly has a maintainer with LineageOS, but maybe they're busy or no longer own the phone.
Unfortunately, I believe the supported phone is the Nexus 5. The 5X is not a different version of the 5, it's the next generation of the smallest Nexus phone line, since the "6" was already taken. The numbering went Nexus 4, 5, 5X.
You can actually get under $100 if you compromise the specs just a little.