Some trs80gp features are only available through the command line. The
easiest way to run from the command line is use the open command.
For example, here is how to start trs80gp in Model I mode with the PCG-80
programmable character graphics generator enabled:
open trs80gp.app --args -m1 -pcg-80
You can run the executable directly which may be preferable in some cases.
Just use the path to it inside the trs80gp.app directory. Here's how to
start a Model II in turbo mode:
trs80gp.app/Contents/MacOS/trs80gp -m2 -turbo