New Security update to Mac OS Catalina solver eGPU boot on mac mini
remember to update without the eGPU connected
After the update the mini will return to a sound at boot and show an apple symbol then the purple stripe and log one screen
Seems this one sorts out the old issues
did you try to update without unplugging the peripherials?
I forgot to unplug all connected equipment (PowerColor Mini Pro, Akitio SK-2520 raid controller, Satechi USB-C Hub) before updating to MacOS 11.1 - and it worked.