Error with field 'AdminPasswordClear'. Invalid username or password or error connecting to Office 365. Powershell is not enabled on the local host or a remote Exchange session cannot be opened on 'outlook.office365.com'. (4379967)

When attempting to save your Office 365 Forest settings by clicking 'Finish', the following error will be returned if MFA is being forced on the Office 365 migration admin account.

Error with field 'AdminPasswordClear'. Invalid username or password or error connecting to Office 365. Powershell is not enabled on the local host or a remote Exchange session cannot be opened on 'outlook.office365.com'.

Either MFA is set directly on the Office 365 migration admin account within the Office 365 portal or is being applied through a Conditional Access Policy. 

Check the Office 365 migration admin account to verify MFA is not applied either directly on the account itself or being assigned through a Conditional Access policy.  

If the Office 365 migration admin account has Multi-Factor Authentication disabled, then that indicates this account is not excluded from some Office 365 Conditional access policies that assign/enable MFA.

The account used to access the Office 365 Forest needs to be excluded, from these conditional access policies.
 
Once MFA is fully disabled from the migration admin account, verify that a login from a web browser does not challenge for MFA and then try to save the Office 365 Forest settings again.