Android (the Android Open Source Project) itself is not the Problem. It's the lock-in ecosystem that Google tries to establish with the Google Services Framework, Play Store and the like. What is missing, is an open and privacy-friendly alternative to GSF. Without GSF we don't have efficient push notifications (Firebase Cloud Messaging), a geolocation provider, a maps API etc.
Personally, I have been using microG (https://microg.org/) instead of GSF on my phone for many years now. However, that is still just a partial solution. While it does its best to be privacy-friendly and does not have any integrated tracking / analytics like GSF, it still has to use Google's servers for push notifications, thus tracking is still possible to some degree.
microG is certainly not perfect and I wouldn't recommend it to the average user. Expect some things to not work or even certain apps to crash. It's a techie-solution for people who value their privacy highly.
Personally, I have been using microG (https://microg.org/) instead of GSF on my phone for many years now. However, that is still just a partial solution. While it does its best to be privacy-friendly and does not have any integrated tracking / analytics like GSF, it still has to use Google's servers for push notifications, thus tracking is still possible to some degree.