Apple has altered macOS's security sandbox rules such that Quick Look generators can no longer access data other than the file they are previewing.
This means that Raw Right Away's preview generator can no longer access its own preferences file!
Apple describes the problem as a "known issue for which there is no known workaround at this time."
Raw Right Away has a workaround, albeit an unconventional one: it supports an alternative method of setting preferences by means of a code number inserted by the user into the Raw Right Away application name.
To set preferences under Big Sur, you literally rename the program.
The new file name is shown in the preferences dialog. As you change settings, the name is updated in real time. When you are finished, manually rename the application as instructed by the dialog.
I recognize this is a hassle, but at least it allows the application to remain configurable until Apple can address this issue.
Renaming an application can confuse the macOS Launch Services database, which may take a few minutes to update itself.
For this reason, Raw Right Away previews may be temporarily unavailable after renaming. If you log out and back in again, they should work.