Please refer to this MS document:
Standalone instances should use the default virtual account, NT Service\MSSQLServerOLAPService for the default instance, or **NT Service\MSOLAP$**instance-name for a named instance.
In my test environment, I reselected the test account and clicked 'OK', and the service restarted.
Default virtual account does not require the password.
Best regards,
Seeya
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