Login As Experience User button not visible for internal Users

1.Under setup->Profiles->App Permission -> Manage External Users should be checked.

2.Object Level Access to Account is set to Edit

3.Record Level Access to Account is set to Edit

4.Community Membership (internal user is a member of the community via permission set or profile access)

Note:
“Edit” access on the Account is not required if the internal user logging in has a role that is higher than the Partner or Customer user they are logging in as. In this case, role hierarchy access is sufficient for the Login As Experience User button to be visible.