There is a related previous discussion at Office/Outlook 365 will no longer support Basic Auth by Oct 1st, 2022 · Issue #3196 · deltachat/deltachat-core-rust · GitHub
Delta Chat will likely drop XOAUTH2 support completely in the future. Gmail is pushing applications to use Gmail API instead of IMAP: OAuth 2.0 Mechanism | Gmail | Google for Developers The other provider Delta Chat supports OAuth 2 for is Yandex, but it is not usable because it asks users to open the browser and solve captcha when they hit some rate limits.
Problem with OAuth 2 is that it requires pre-registering Delta Chat with each email provider and hardcording OAuth 2 authentication URLs into the application. This option is limited to large providers and they can always decide to change requirements and unregister the client.
There are two approaches that try to fix OAuth 2: