NVRAM

Nonvolatile random-access memory (NVRAM) stores certain system settings across restarts. Depending on the Mac, these can include display resolution, sound volume and startup-disk selection. Apple’s NVRAM explanation

BetterDisplay can offer NVRAM clearing alongside a macOS display-settings reset. This is broader than forgetting a display in BetterDisplay or resetting the app's own preferences.

See Displays Overview for the reset choices and their scope.