The purpose of buying a OnePlus device is to get decent hardware for an okay price (I have the 3T), and then take advantage of their unlocked bootloader and the multitudes of highly functional kernels for it. Sultan's LineageOS ROMs are quite nice and even include WireGuard. If you're not immediately removing non-free OxygenOS when you receive your phone, you're most certainly already doing it wrong, data collection or not.