[thewavelength]

As of my knowledge, you can log in to Skype without 2FA using an outlook.com-email-address even though it has 2FA enabled.

[hpshelton]

If you have proof of a repro for this, please reach out to our security team(s), but to the best of my knowledge this is false. 2FA works on both regular and merged Skype and Microsoft Accounts on all endpoints.