Hi @Regreener ,
It's also suggested to check the instructions in the document below and make sure the cmdlets you used to connect to Exchange Online powershell are proper:
Connect to Exchange Online PowerShell using modern authentication with or without MFA
Especially ensure that you are using Connect-ExchangeOnline rather than *Get-Credential** to pass the account's credential, as the Get-Credential cmdlet doesn’t support MFA enabled accounts and may lead to the error you encountered according to the article below:
Connect to Exchange Online PowerShell without Basic Authentication
(Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)
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