@CaseySJ Want to update that the ATEN 7220 Thunderbolt Switch (TB2 with Apple TB2->TB3 adapters) is working well on my flashed Designaire running Catalina. The unit can be hot plugged. USB and display (DP and HDMI) work well. Unable to get it to work on the first Big Sur Public Beta.
Update Aug 13: After some time, the TB connected display started blanking out every 30-90 seconds. Installing Amphetamine initially helped, but the problem returned during CCC backups. Logfiles showed multiple errors coming from Spotlight. I realized that I had not excluded the Big Sur volumes from Spotlight, but the problem remained after exclusion (in retrospect, I should have rebuild the index but forgot).
Since Big Sur does not work with the ATEN 7220 in my testing, I decided to simplify and removed the Big Sur volume and uninstalled Amphetemene. The problem has gone, Spotlight errors are absent, and the system is working as expected (which is great if you want to share a single high quality display/camera/audio setup with two servers). At some point I will try again with Big Sur, but am 'stuck' on Catalina for the moment.