anarchosax Please advise.
Looking back at this thread, it seems as if when you re-flashed Google's OS onto the phone it went for a day or two without SIM PIN problems, then you went back to GrapheneOS for nine days and it also didn't have SIM PIN problems, but now it does. If there is a problem with the phone hardware involving the SIM tray, but the problem doesn't show up daily, that might be provable by switching back to Google's OS for a while (say, a month). If doing that, it might be good to subscribe to a beta-release channel, in case the issue is somehow triggered by updates.
Another option might be trying a different SIM card. This might help even if nothing is outright wrong with the SIM card -- it is possible that the SIM reader in your device is a little marginal and that makes it picky about SIM cards that themselves don't have something outright wrong about them.
A third option might be switching to an eSIM. If there is a problem with the physical SIM reader but not the eSIM chip, that could be helpful. On the other hand, if there were a hardware problem "higher up", then ejecting the eSIM might not be an option, so you might in theory end up completely locked out of the device.
If it sounds as if I'm trying to figure out which piece of hardware to blame, that's because so far the symptoms sound consistent with an intermittent hardware problem, and meanwhile other users are not reporting similar problems, which (as other8026 points out) would be expected if this were a software problem.
Which carrier are you using?