Just found a webapp that does just that

https://20-20-20-timer.netlify.app/

If anyone needs it in the future

Ill have a look cheers!

I don’t know of such a FOSS app

Not to be an ass, but that’s what I was asking about

I used to have an app and it would count 30s every 30 min and I didn’t have to press anything to reset it. It also had an option to vibrate rather than beeping (within app not phone wide)

I cant achieve that with a timer

No