> I still keep in a drawer an old OnePlus 5 I bought in 2017 with a pristine Android system.

How pristine is that when the last supported Android version is 10?

> This phone is sometimes necessary. Like when a known bug in /e/OS prevented my banking app from working for several months.

This surprises me. Until very recently I was using a phone I bought in 2017, which similarly supports no Android beyond version 10.

Since early this year, my bank app started insisting that I upgrade my Android to 11 or higher, and hence stopped working.

More recently, Gmail also started insisting I upgrade Android. As a result I had to get a new phone, which in many ways is worse than my old phone (still 7.2" but worse aspect ratio, no more full fingerprint sensor and much worse battery life).

So the idea of keeping an old phone around in order to bank seems rather odd to me.