Computer Configuration > Administrative Templates > Microsoft Edge > Identity and sign-in
Both
HKLM\Software\Policies\Microsoft\Edge
This policy only takes effect when the 'WebToBrowserSignInEnabled' (Web To Browser Sign-in Enabled) is enabled. If this policy is enabled, users cannot turn off Seamless Web to Browser Sign-in feature from "Automatic sign in on Microsoft Edge" setting on Microsoft Edge profile settings page and that toggle will be greyed out. If this policy is disabled, users cannot turn on Seamless Web to Browser Sign-in feature from "Automatic sign in on Microsoft Edge" setting on Microsoft Edge profile settings page and that toggle will be greyed out. If this policy is not configured, users can turn on/off Seamless Web to Browser Sign-in feature from settings by themselves.