I also encourage people to check if their devices are supported by LineageOS when they run past their support period, it can be a good way to keep getting security updates past official support windows.
The forums should list some caveats for the device if they exist, but don't assume just because it shows up on the list that everything will work perfectly out of the box -- double check to see if there are any downsides.
Also, I should bring up that LineageOS comes in two variants: one without Google services and one with Google services. If you want to actually de-Google your phone, check to see that you are not going to run into problems with the apps you use.
Occasionally I see people who don't realize how deep Google services can go on Android, which in some ways gets back to your argument about how "open" Android really is. So it's just good to make sure that your stuff will all work afterwards if you're planning to go down that route.
Sure, if you're so laser-focused on privacy that you want some obscure phone which will do nothing aside from text, call, and send Signal messages, go buy the weirdest one you can find. otherwise you won't be finding anything remotely enjoyable if it's not iOS or a major android flagship. And out of those options, only one respects the user's privacy and security.
Ok, come on. What apple’s done here is great, and I personally use an iPhone, but you couldn’t think of a good reason to use anything else? An open-source OS?