According to this change Office 365 should support email aliases using the + sign since September this year: https://www.microsoft.com/en-us/microsoft-365/roadmap?filters=&searchterms=59441
I have tested the feature on 2 office 365 environments, but in both cases Office 365 returns that it cannot find the user. [username]+[tag] wasn't found at [domain]
Am I missing something?