That would be the safest approach.
There is a post in one of the 21.02rc? threads that indicates apparently only the system and network files need to change in /etc/config/. Perhaps through an unrelated error I introduced without realizing it, but I was not able to copy backups of my other files (firewall, wireless, etc.) into /etc/config/ and get everything working. So this is why I suggest safest approach is to just start over from scratch.
Edit:
Took me longer than I thought. Here's the post about only keeping the new network and system files and using your prior setup files for the rest, but like I said, might be safest to just start from scratch.
https://forum.openwrt.org/t/openwrt-21-02-0-first-release-candidate/95039/26?u=eginnc