Your time has come: https://forums.oneplus.com/threads/oxygenos-11-0-9-9-for-the-oneplus-8-and-oneplus-8-pro.1510769/At this point I've done about 3 dirty updates via system update. So I'd be heading for a clean install anyway.
I have no emulators set up and thanks to @AnierinB Google photos is unlimited, so I don't have a risk really.
I'd always stick with the latest firmware as it could potentially affect more than just the OS iirc it was a requirement in the past for custom ROMs or issues could ensue.
I'd be updating, nuking the OS then going Evo X via twrp..I'll defo make a guide, step by step, hopefully itll cover more than just Evo so others can use it.
Right now Evo had me coveted, I have about 2-3 issues but not deal breakers. Battery also could definitely be improved.
Overall though its a stellar ROM.