It's not the OS that is transmitting the data over to Google, but rather OpenGapps (ie. Google Play). OpenGapps is software that can be optionally installed after the initial installation of LineageOS (but before first boot). A user can still use LineageOS without OpenGapps, though they just won't have the benefits (and drawbacks) that come with it (such as being able to use apps that require GSF). The user can instead opt for an app manager like F-droid or possibly Aurora Store.
In addition, there exists an alternative to OpenGapps called MicroG. This is like Google Play but allows users the option to anonymize themselves. One can find custom LineageOS builds that include MicroG from the MicroG website (as the members of the LineageOS project do not advocate for its use, instead giving preference to OpenGapps). Keep in mind, however, that there are fewer devices supported by those builds.
In the cited paper (https://www.scss.tcd.ie/Doug.Leith/Android_privacy_report.pd...), the device used to test LineageOS was a Google Pixel 2 running LineageOS 17.1 which also included an installation of OpenGapps 10.0 nano.
It's not the OS that is transmitting the data over to Google, but rather OpenGapps (ie. Google Play). OpenGapps is software that can be optionally installed after the initial installation of LineageOS (but before first boot). A user can still use LineageOS without OpenGapps, though they just won't have the benefits (and drawbacks) that come with it (such as being able to use apps that require GSF). The user can instead opt for an app manager like F-droid or possibly Aurora Store.
In addition, there exists an alternative to OpenGapps called MicroG. This is like Google Play but allows users the option to anonymize themselves. One can find custom LineageOS builds that include MicroG from the MicroG website (as the members of the LineageOS project do not advocate for its use, instead giving preference to OpenGapps). Keep in mind, however, that there are fewer devices supported by those builds.