That should not happen, of course. I mean, I got a cheap chinese watch off AliX with such a strap and while I had my qualms, it held on. Are you sure you’re fully seating both pins?
Two solutions: warranty claim, or get a regular non-quick-release setup.
I ran e/OS on an old OnePlus for a year, quite close to GrapheneOS and mostly just as free of Google. There are plenty of options out there to run a degoogled Android these days.
But yes, running GrapheneOS on a brand new Pixel Pro right now, couldn’t be happier.