Has anyone had any issues with getting the Yamaha USB drivers to work with MODX Connect ?
My MODX works only when I uninstall the Yamaha drivers but the MODX Connect software remains disconnected.
Ironically, if I install the drivers, the MODX Connect software sees the keyboard, but I lose sound everywhere else.
Just curious if anyone else has seen this too.

The MODX works with just one Driver (singular), it is called “Yamaha Steinberg USB Driver v1.10.5” compatible through Mac OS 10.14 (Mojave).
The Yamaha USB-MIDI Driver is not compatible with the MODX.
We are not certain what “drivers” (plural) you are referring to, but an update for Catalina 10.15 has not been released.
In the meantime, verify you are set to use the MODX as you Mac’s INPUT and OUTPUT device
In System Preferences > go to Sound > select MODX for both the Input and Output tab.
In general, it is always recommended to hold off on updating your computer’s OS until the compatible driver for your music gear becomes available... that is pretty much true across the board with any music production gear that you own.

I've had to uninstall drivers frequently to get past the soundmondo bug. I've never had to download the old version of the driver. The instructions I left work without having to get the 'old driver' package. Windows keeps the uninstall/setup for everything it installs and allows access to this from the 'Add Or Remove Programs' feature. Also available through the Control Panel but labeled as 'Programs And Features'.
The 'Programs And Features' method uses the old windows style that should look familiar from Windows Vista/7/8. The other method I gave, 'Add or Remove Programs', is the newer style 'Metro' interface that was introduced with Win 8 and since has most system-level Windows applications moving to this kind of interface. These also respect the 'dark mode' while the older style apps (such as 'Programs And Features' ) do not.
Not to say the above is the bible ...
I guess it's possible that somehow you could try to remove drivers by milling around your filesystem and deleting files manually without doing a true uninstall. Depending on what you delete (i.e. corrupt) - you may end up trashing the uninstall which may be resolved by either downloading the old driver - or just doing an in-place install of the newer driver which should prompt you to uninstall the old driver if the stars align.
If this is how you got there (manual deletion) - then don't do that in the future. Around the Windows NT introduction days, we would 'affectionately' call Windows 'Windows Jr.'. As frequently Windows would corrupt and the easiest way to resolve would be to 'JR' - just reinstall. Similar pessimistic product acronym humor as 'FORD'.