While converting to Visual Previews, DNG Converter is extremely slow and leaving dozens upon dozens of DNG converter icons open in my dock, overloading my system, no other apps can function. I have to Force quit LRT. It list DNG Converter as (not responding).

I've been using LRT for about 6 years and never have had this problem. I'm running LRT Pro 5.4 Build 619, DNG Converter 12.2 on MacBook Pro OS X Catalina

With Catalina Apple changed a lot and added some stupi security annoyances.
Try allowing LRTimelapse and the Adobe DNG Converter full Disk Access as explained here: https://forum.lrtimelapse.com/Thread-wil...-and-later
If that doesn't help, reduce the number of parallel threads in the LRTimelapse Expert settings.

I reduced the threads from 12 to 10 and it does seem to help. I guess I'll just have to live with the slower Preview generation. Let me know if any updates are made to this in the future.

Please check the log, if you get any timeouts - that's not normal then. Normally generating the visual previews on a recent computer is quite performant if all goes well and the OS is not blocking the process.