I have finally got a VM of Catalina up and running for testing. Apple's decision to drop all 32-bit support is a real pain.
Still - I have now got new versions of ctags, avrdude, and avr-gcc up and running that work on Catalina. I guess that ARM based boards should be my next target for investigation. I know that PIC32 is going to have to wait until Microchip finally provide us with an updated compiler that's built for 64-bit.