Recently had a user who could not log in to their microsoft Teams , due to the blank login whitescreen loop

1. Try rebooting the PC always as sometimes SAML crashes

I had to clear the Application Data Settings : 

Close Teams.exe and Outlook.exe processes

Delete the Folder :

C:\Users\%username%\AppData\Roaming\Microsoft\Teams

or you can script it granularly : 

Get-ChildItem -Path $env:APPDATA\”Microsoft\teams\application cache\cache” | Remove-Item -Confirm:$false
Get-ChildItem -Path $env:APPDATA\”Microsoft\teams\blob_storage” | Remove-Item -Confirm:$false
Get-ChildItem -Path $env:APPDATA\”Microsoft\teams\databases” | Remove-Item -Confirm:$false
Get-ChildItem -Path $env:APPDATA\”Microsoft\teams\cache” | Remove-Item -Confirm:$false
Get-ChildItem -Path $env:APPDATA\”Microsoft\teams\gpucache” | Remove-Item -Confirm:$false
Get-ChildItem -Path $env:APPDATA\”Microsoft\teams\Indexeddb” | Remove-Item -Confirm:$false
Get-ChildItem -Path $env:APPDATA\”Microsoft\teams\Local Storage” | Remove-Item -Confirm:$false
Get-ChildItem -Path $env:APPDATA\”Microsoft\teams\tmp” | Remove-Item -Confirm:$false

Try reopening Teams , if not delete the below

C:\Users\%username%\AppData\Local\Microsoft\Teams

Reinstall Teams and Sign out  and sign back in at the user