We used to use the androidx compiler at some point, but then we had to add some patches for k/js and k/native (caused by k/native and k/js differences comparing to k/jvm). We tend to upstream them asap, but last times we published our builds.
The thing is that androidx doesn’t test against k/js and k/native, so we can catch the bugs and issues only after a new androidx version is available. So we fix them on our side and then we upstream.