Er-Force sim has moved to qt6.
Step 2 should read:
cmake protobuf-compiler libprotobuf-dev qt6-base-dev libqt6opengl6-dev g++ libusb-1.0-0-dev libsdl2-dev libqt6svg6-dev libssl-dev libglu1-mesa-dev
It currently reads:
sudo apt install cmake protobuf-compiler libprotobuf-dev qtbase5-dev libqt5opengl5-dev g++ libusb-1.0-0-dev libsdl2-dev libqt5svg5-dev libssl-dev
Taken from their updated readme which landed last month.