I used to run with AirPods multiple times a week, and used them while walking around and on public transit. I've done the same with AirPods pro borrowed from my S.O.

Did they ever fall out? Only a small portion of the time. Half the time I noticed it and caught them.

Was the idea of them falling out stressful? Hell yeah. Nothing like a $50+ bud to stress the hell out of you when you're trying to get a run in and it just will. not. sit. in. your. ear. correctly. Add sweat to the equation and things get messy quick. And the fact that in some places, like public transit, you have a good chance of losing the bud forever if it falls out.

I am much happier with the IEMs I've been using for a half a year or so now. They hook over my ears optionally, so they're never really in danger of falling out and I never have to mess with them. And they're wired to me anyway even if they do fall.

I have Pixel Buds and I haven't tried running with them yet (it's been cold since I got them for Christmas).

I used to run with Bluetooth over-ear headphones, which was great in winter, and, uh, less great in summer (the foam would get completely soaked and foul-smelling).

The ear supports on the Pixel Buds are pretty secure, though, I expect it to be OK, especially at my pace.

I can shake my head around like crazy and my airpod pros don't fall out. Never had them fall out running which I try to do 3 times a week either.

Nope, if AirPods fit your ears they stay in. I have first gen set that I still use for biking and big drops or bumps have zero effect.