Here is was what happened:
I installed the latest version, PreSonus_UniversalControl_v3_5_0_64605, onto Big Sur 11.4 Intel, and it worked, until that is I restart my computer. After that, the Thunderbolt indicator light flashed blue and the power button was a solid red. I tried everything that Presonus recommended, including all the security measures and re-installing.
I even reduced the startup system security to medium in recovery mode, hoping that it would allow the kernel extensions to work properly. No good.
Here's how I fixed it:
Just as user ianlehmann recommended, I uninstalled the latest version, restart the Mac, then installed an older version of Universal Control, and finally restart again, and it worked!
I specifically went back to PreSonus_UniversalControl_v3_4_2_63992 from March 2021.