I have done my Mojang to Microsoft account migration today. After that I'm not able to login into the Launcher anymore. As soon as I click on the "Microsoft Login" Button the launcher asks for a USB security key. I have never set up such kind of a key and I'm also not able to select the Other ways to sign in button.
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This appears to be an account related issue and the bug tracker does not have access to the appropriate resources to help you with this problem. Instead, please contact Mojang Support in order to receive assistance, regarding your concern.