Official announce from Steinberg:
https://www.steinberg.net/en/newsandevents/news/newsdetail/article/steinberg-products-incompatible-with-macos-catalina-5225.html

User forum discussion:
https://www.steinberg.net/forums/viewtopic.php?f=157&t=168116

"End of October" is either here or around the corner. So any day now - there should be some form of update. Either an announce of some date in the future or the driver update. Since it was absolutely known that there would be a gap between Catalina release and availability of a Yamaha Steinberg USB Driver that was compatible - the suggestion from Steinberg has been to delay updating your operating system. If you've already updated or have not and delaying update is not feasible - then there will be a gap where anything depending on the driver will not work properly. The behavior reported by several is that the end result will be "no sound".

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.

Thanks for the feedback both Jason and Bad Mister. I definitely knew the risk, I was just surprised no one else had asked about it. Regarding other drivers, merely removing the existing Yamaha drivers causes my the MODX audio interface to function properly (except regarding MODX Connect) for some reason. Installing them causes the MODX Connect software to detect the keyboard ( "Online" ) but I lose sound throughout the system.

For the time being it appears I just have to do without MODX Connect until the new drivers are released.

I understand many AU items are left out (go Apple!)

Finally an update:
https://www.steinberg.net/en/support/downloads_hardware/yamaha_steinberg_usb_driver.html

I've confirmed restored functionality of MODX Connect w/ sound.