Yes, it is not supported, but this is on the todo list (as I have read
recently) to be implemented, because it is widely used. I don't think it
will get done before 14.2.
OAuth2 support is something we will look into in future.
For the time being, you may want to try out using this proxy app, which should make OAuth2
server available for
non-OAuth2-ready applications. I haven't tried it myself, but that is what it says on
the website.
https://github.com/simonrob/email-oauth2-proxy/tree/main
If you try it, please let us know how it goes.
Cheers
Michele