I exported and backed up all my rules before deleting and recreating my Catalina SSD volumes, then performing a clean install of Big Sur. On downloading the Hazel install file and running it I installed the application by clicking the install icon in the dialog. I didn't let Hazel create the default rules, so I ended up as expected with a Hazel window devoid of folders and rules. I attempted to import rules, and things went south from there. The Hazel window didn't display the rules, yet I could see the folders if I selected the preview window. I uninstalled and reinstalled. No luck. Eventually ended up with a gray Hazel window with no folder or rules columns and no rules. The options to create folders or import rules were gone. With nothing to lose, I went to preferences and tried different layouts to see if I could get some sort of ui in the bare gray Hazel window. In doing so, I checked the trash checkbox in preferences. As a result, I was prompted to give full disk access to Hazel. This fixed my problems. I went back and created my folders and imported my rules. A quick test shows the rules are working as expected now.
I thought I'd share in case it helps anyone else.