As far as I know, microG only sends data when Device Registration/google login is turned on, Push Notifications in microG are enabled, and through UnifiedNLP (location services). Data gets sent to Google through unifiedNLP due to the fact that the Secure User-Plane Location (SUPL) provider in Android's gps.conf file is Google. There is a Magisk module to replace the SUPL provider, but again that requires root.

MicroG doesn't install a usable version of Google maps, and I wouldn't try to install one if using microG. I am unaware of what data Google Speech Synthesis/Recognition sends if anything (I have it blocked from having internet access using a root firewall as a precaution).

The e/OS team has tried to strip every bit of Google out of Android, but getting everything out is hard. Putting Google stuff back in is fine if you know and control what data is being sent. I accept the tradeoff of potential data being leaked when using Android Auto because I have much of it blocked from internet access, but that also might be why AA eventually stopped passing the security check on my device.

As I said, I have no single Google apps and this work. I just don't have tts and voice recognition, but one can easily do without, furthermore if you have someone by your side that can reply for you or you can wait a break to reply to messages. I have apps to have the map, my music, my podcasts, my audiobooks, all available on my car interface which is enough for me.