I migrated my account from mojang to microsoft. The OLD launcher works as expected.  The new one however just spins the "waiting" animation when I click the "Microsoft Login" button, I see a brief flash of the panel to enter credentials but is gone instantly (no it is not in the background). What I have tried:

-Making sure it is not blocked by Firewalls

-Making sure the login dialog is in the background somewhere.

-Unistalling the old launcher

-Reinstalling the new launcher (and rebooting several times).

-Closing all other apps

-Looking in the event viewer for errors (no errors or warnings).

I eventually uninstalled it the new launcher and reverted back to old launcher (which worked instantly).