@Justin Lee, Thanks for posting in Q&A. Based on the information provided, it seems that the issue with not being able to sign in with a username and password on devices enrolled in Intune using M365 credentials might be related to the Windows Hello for Business settings. To allow users to sign in with a username and password, Windows Hello for Business needs to be disabled. You can check if we have the following policy configured in Intune which enable windows hello for business. If yes, set it as disable to see if it works.
Please check the above information and if there's any update, feel free to let us know.
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