A notable mention is https://ubports.com/en/ which is different from postmarketos in a sense that ubports uses old kernels with heavy patches. That means: good support for things, but difficult future.
PostmarketOS uses the newest kernels and tries to integrate their patches into mainline kernel, so that the reliability is maintained with all kernel developers.
Same. I still have my previous phone, but I don’t use it anymore because it’s insecure, not because it’s broken. I’m still using a laptop that’s even older precisely because it gets security updates since it runs Linux.
I’d absolutely lay a premium for longer support and it’s a large part of why I got a Pixel this time around, they advertise 7 years of support and I hope to hold them to that.