area51 I also read that, but not having changed from Stock Pixel OS with an eSIM to GrapheneOS, its hardly a claim I can use, have you personal experience in doing so.
The claim is true. I've flashed from stock to GrapheneOS multiple times without my eSIM being wiped. Worked fine. Note that eSIMs are stored on a dedicated chip called eUICC, and there's no reason for a flashing process to wipe it anyway. https://en.m.wikipedia.org/wiki/ESIM