Maybe the battery. I’m typing this on my 13 mini and it’s as fast as it’s ever been.

I still have apple care+ on mine. I knew they will probably never make a new one again. I use it without a case, so when I drop it break the screen or something, I just get an express replacement. There is a small fee ($100 or something) and I basically get a brand new iPhone mini. Hopefully their replacement stock last for a while.