I have a 9Pro that was really great on Oxygen OS 11. Then ~~Oneplus~~ Oppo dumped ColorOS 12 and 13 crapware on us and T-Mobile forced upgrades.
The bugs in ColorOS often make the phone unusable. ALL my program icons regularly are just missing from the screen when the phone's unlocked and it only shows the wallpaper. The display either won't shut off or shuts off while I'm using it. The fingerprint reader icon randomly disappears when trying to use it or just doesn't show up at all. I hope I never have to dial 911 with this POS because there's a good chance I won't be able to.
The hardware's fine but that makes no difference at all without a usable OS, and there is no way Oppo is going fix anything. Last Oneplus phone I buy.
The purpose of my first Oneplus phone purchase years ago was that OxygenOS worked just fine without dealing with custom ROMs, but ColorOS's bugs are so severe I'll end up having to load Lineage or an AOSP distribution. Hopefully Google will sort out enough of the bugs by the next version to make a Pixel a good choice.