Talcum0094 I have about 10 apps I use on my main profile... if I install google play services and play store on my main profile... will google be able to see that I am using (for example) whatsapp? can it see that I have signal running? proton mail?
Yes, they can see all apps you have installed in that profile, even if they were installed from another source. I am pretty certain that is how they check for updates, they fetch the list of all apps you have installed in the profile, and then query their server if that app is on Google Play and with a newer version. Otherwise they would have to download a repository list of all apps to your device to not leak that information, and they appear to not do anything like that.
Talcum0094 So, if I use an anonymous google accoutn and throiw it in my main profile.... what level of privacy am I giving up exactly?
That they will know what apps you have installed, pretty much. And what kind of Pixel device you have. And that you are running GrapheneOS.
As long as you do not give them any specific permissions, they won't be able to read your files, spy on your app usage, read your contact list, read your messages or anything like that. They also cannot update apps you have installed that aren't the Google Play version of the app, since they do not have the signing key needed to do that. So it is generally safe to have Google Play with Play Services installed on GrapheneOS from a privacy point of view.