There's a closed pull request on the void-packages repository

New package: cyrus-sasl-xoauth2-0.2.
https://github.com/void-linux/void-packages/pull/22206

Description:
This allows one to utilize XOAUTH2 with `mbsync` and `msmtp`, which will be necessary for accessing Google mail servers in the near future.

There is a small patch needed with `isync` to take advantuage of this, but it is already upstream and should be in the next release.