Computer Configuration > Administrative Templates > Microsoft Edge - Default Settings (users can override)
Both
HKLM\Software\Policies\Microsoft\Edge\Recommended
'Allow single sign-on for Microsoft personal sites using this profile' option allows non-MSA profiles to be able to use single sign-on for Microsoft sites using MSA credentials present on the machine. This option shows up for end-users as a toggle in Settings -> Profiles -> Profile Preferences for non-MSA profiles only. If you disable this policy, non-MSA profiles will not be able to use single sign-on for Microsoft sites using MSA credentials present on the machine. If you enable this policy or don't configure it, users will be able to use the Settings option to ensure non-MSA profiles are able to use single sign-on for Microsoft sites using MSA credentials present on the machine provided only a single MSA account exists on the machine.