So recently I’ve been seeing the trend where Android OEMs such as Google, Samsung, etc. have been extending their software release times up to like five, six, and seven years after device release. Clearly, phone hardware has gotten to the point where it can support software for that long, and computers have been in that stage for a very long time. From what I can tell, the only OEM that does this currently might be Fairphone.
Edit: The battery is the thing that goes the fastest so manufacturers could just offer new batteries and that would solve a lot of the problem.
How does the postmarket OS work? Is it pure Linux? Does it support android apps?
Yes, it pure linux and is based on Alpine linux often used in Docker Containers. Many supported devices run an upstream kernel instead of the old manufacturer one that comes with android. Android apps can work though waydroid, though I have not used apps that require google play services, though I did get that working on my laptoo.