We are all up and running again.
My solutions:
Computer 1: Desktop. GeForce 710. Latest Proprietary Drivers were installed and working. Stuck at "Loading Application Resources". I had to install libopengl0 and libcanberra-gtk-modules
sudo apt install libopengl0
sudo apt install libcanberra-gtk-module
Computer 2: Desktop. Previously with AMD Radeon Card. Stuck at "Loading Application Resources" Had message "radeon: Failed to get PCI ID, error number -13".
Problem solved in a "rather direct fashion". I removed the Radeon card (which also had a noisy fan), and bought an NVidia GeForce 710 card. I installed the 460 proprietary drivers. Did not have to install anything else.
Computer 3: Laptop with Built-in Nvidia. NVidia 440 drivers installed, but not being used due to EUFI. Stuck at "Loading Application Resources". Had to install 460 drivers from the command line. Doing so did the EUFI stuff. Did not have to install anything else.
Computer 4: Laptop with Built-in Nvidia. NVidia 460 drivers already installed, but not being used due to EUFI. Did a regular Update through Software Updater. Doing so made the EUFI MOK stuff happen. I had to install libopengl0 and libcanberra-gtk-module as with Computer 1.
08-Mar-2021 01:27:07