Welcome to the nightmarish world of authentication to Google products, which all have 4 different versions of documentation and not a single one up to date.

For auth it seems the preferred way to login with Google is OAuth2, that's I believe what third-party apps use, e.g. Thunderbird uses it when setting up a new GMail account.

However, for apps that don't support OAuth2, there is also the possibility of using "App Passwords" [1], I've used one in the past and it worked well. (Update: I'm just reading it only works if 2FA is enabled, which I use)

[1]: https://support.google.com/accounts/answer/185833?hl=en