Protonuser I'm not sure what the exact process is, but GrapheneOS has recently made some changes what happens when the phone overheats.
See this release: https://grapheneos.org/releases#2024012600
kernel (Pixel 6, Pixel 6 Pro, Pixel 6a, Pixel 7, Pixel 7 Pro, Pixel 7a, Pixel Tablet, Pixel Fold, Pixel 8, Pixel 8 Pro): use a normal reboot on overheating instead of an emergency reboot to harden against physical attacks
Also, you can read through this thread by the official GrapheneOS project account: https://bsky.app/profile/grapheneos.org/post/3kjwsklnrjs2f