and Login to outlook.com doesn’t require you to use 2fa? If it did prompt you (and Duo entered some otp I guess?) and login worked, I’m pretty sure it’s the token hand back from Browser to Mail that’s still at issue to add your outlook.com Email to the default Mail app.
An unlocked bootloader only relevant if the Authenticator App wants to enforce some property of it - Duo Mobile works reportedly (the backup/account transfer feature though doesn’t).
I think it’s a gamble to use corporate-y Apps with microG frankensteins. If it works, it works until it doesn’t, and then who you gonna call.