I recommend you to root your phone. With a rooted device you can debloat your phone very easily with UAD (universal Android debloater) for example. Delete any Google related app and of course any diagnostic app from OnePlus. After you deleted Googles apps including gms (!) You can install microG via an magisk module named microG installer for magisk. You don’t need the Playstore, use Aurora instead. But first search on Fdroid if there is an opensource alternative for what you’re looking for.
All of this might take an evening, but after it, you have peace of mind. Note that for root, you’ll have to unlock the bootloader. This will wipe your data, so do a backup beforehand.
If you want to, I can give you a more detailed guide.