* but I have to admit that the hardware is quite slow
It is because computers run one of a few available OS's. The OS is being maintained by the distributer (MS, Apple, Google) and your hardware is good as long as the drivers are still receiving updates.
Phones are different because even though everyone only uses iOS or Android, every Android manufacturer puts their own layer onto Android, so Google can continusously update it but the manufacturer might not. Most companies only maintain their phones for about 3 years, giving a significantly reduced lifetime than computers.
It still works fine, from from a security perspective, keeping the phone without patch support is a bad idea.
It is really annoying how every vendor cobbles together a Frankenstein abomination of a kernel with just the right drivers and patches and good luck trying to run anything else. But I also understand that they (except maybe for Google) have no interest or incentive to clean up this mess.
Fairphone 5 will receive security updates for 8 years
Pixel 8 will receive updates for 7 years
iPhone 15 will receive updates for 6+ years (apparently, Apple has a track record of between 6 and 8 years)