I'm not as old as everyone else here is mentioning, but started having this issue a few years ago with my phone. My fix was to rub my hands together for a few seconds. Don't know why but it's always worked for me.

I'm curious if you have issues with pulse oximeters too. The thing they use to check your blood oxygen level when you go to the doctor.

I don't tend to have the issues everyone here is talking about, but those things never work for me on the first try.

Those work off light absorption, so different mechanism.

Understood, but idly wondered if there's a correlation between people with one issue and the other.

I don't remember, it's been a long time since I've seen one.

Or lick the back of your hand and then moisten the finger on that. More discreet and more hygienic (well, hygienic for you at least).