Try restarting your X server (or Wayland or whatever) first if you haven't done so, just in case flushing any surviving copy of the old llvm .so out of memory does the trick (unlikely, but it can't do any harm).

If it doesn't, well, the setting has to be stored somewhere, but if it isn't in a plain text file somewhere in .config, you'll need to talk to the people working on Brave to find out which file it is and how to edit it.

The last-ditch method would involve using a symlink to the new llvm .so to trick Brave into thinking the old llvm .so is still there. That may fix the hardware acceleration temporarily, or do nothing, or crash Brave or your system, so probably not worth it in this case. (For most other missing-library cases this trick is harmless, but I'm not sure of the interactions of llvm, mesa, kernel video drivers and the browser in this case.)