Going to bump this question.
I just wanted to say THANK YOU SO MUCH for the awesome guide.
One suggestion I do have is to use TeMeFi rather than either of the magisk modules for detaching (obviously this is for the root version only.) I had been using TeMeFi for a year or two with Vanced, and after I figured out how to do it, it worked very well and didn't seem to impact anything else. I figured I'd follow your guide to the T and while the modules did work to detach ReVanced I also noticed some new system lag. When I removed the modules and used TeMeFi instead, the detaching worked and the system lag was gone.
A couple notes on TeMeFi though.
1. Visiting the YouTube app in the Play Store and hitting the "open" button or "update" button will reattach the app (TeMeFi itself doesn't do reattaching from what I can tell.) After I uninstalled the modules, I needed to reattach before using TeMeFi.
2. The level 3 TeMeFi detachment is the only one that has worked well. The others get broken way too quickly and things start to fail.
3. It's a best practice to check the detach status of YouTube every month or so just to make sure it passes all the checks. It only takes about 15 seconds to check, and another 10 seconds to re-run the level 3 detach, if necessary. Not too shabby (and WAY more transparent than the magisk modules.)
4. If you have any additional issues, the developer is great and seems very happy to reply with detailed responses. Just make sure you do a bit of reading because he will shade you a bit if you ask silly questions lol.
Anyway, thank you again!