[emersion]

Yes. I'd argue the problem is not on the project's side, it's on the Google side (they have ridiculously high requirements for registering OAuth clients for IMAP/SMTP use, especially for a small open-source project).

[htrp]

Any good guide on this (registering oauth clients) for people who want to make the move?

[jpc0]

https://support.google.com/cloud/answer/6158849?hl=en#zippy=

There is likely a package/library for your language of choice to do a basic oauth client.