Changing folder icons on a secondary container/partition was very buggy with 11.0.1. I had to enable root, then copy/paste the icon. It'd work once, but then stop working, so I had to restart completely and do it for the other icons, bit by bit. I suspect this is a bug, because it'd work initially, then stop working altogether until a restart. Non-sensical.
Do you not read previous posts? In my posts #11 and #14 above, I clearly detail that it is moderately easy to change top level system folder icons. I’ve been doing it for every beta of BS and the final public release. If you change volume icons or folder icons, you need to clear icon cache and rewrite various files on the Preboot volume, as well as creating a new snapshot - or else your changes won’t stick. Big Sur is not buggy in this regard. It’s actually being widely reported as stable and very fast, esp. compared with Catalina. Just follow a proven method and try not to reinvent the wheel. I’ve already spent months fine tuning what works and tried everything that doesn’t. Read what I’ve posted above.I ended up just booting into Safe Boot, logging into root instead of my normal account, then was able to change all the icons I wanted to. (I changed the icon for my main Macintosh HD disk, the Data partition I created as a container, and some folders on the Data partition. Incidentally, for the Macintosh HD disk, I used the Big Sur main icon, which you can locate by opening the macOS Installer application in Preview, then selecting a specific icon you want, then copying it. However, for a full guarantee, I used Image2Icon, free from the App Store.) After doing all of this, I just re-disabled root and never had to worry about it again (so far, anyway—hopefully the 11.0.2 or 11.1 update won't undo the Macintosh HD icon change).
It was not without its struggles, though. I can imagine it'd be fruitless/next to impossible to change the actual folder icons in / (top level).