This has been a subject broached quite a few times over the years and not just on Samsung Phone's @FishmanAGD
We all know what Apple did to their iPhone's so that they accepted the newest iOS !
Issues can occur with phones especially if there used for longer periods of time. They accrue broken files, junk files etc and the batteries output tends to decrease.
I personally make sure I keep up to clearing out old files and caches etc and don't download apps that I really don't use or are not productive to me.
Sometimes even the sim card can cause issues hence when you swapped out to Payg this may have helped resolve some problems - who knows
I tend to use a phone for 2 years max and swap out for my own reasons.
In my opinion Samsung don't affect their phones negatively via software and security updates to steer a person to upgrade.
Again my own personal opinion.
🌈 Stay Safe 🌈
Daily Driver > Samsung Galaxy s²² Ultra 256Gb in Phantom Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "