Windows: Simply install the the Windows-Installer package (.MSI-file) suitable for your Windows version.
Differences between the two Windows builds.
If it shows a DLL missing error, you need to additionally install the MS Visual C++ Redistributable Package
from here. See also
this.
Mac/Linux: Install Python 3.8 (or newer) for your platform,
then install MTGProxyPrinter via pip or pipx: pip install MTGProxyPrinter.
The launcher will be named "mtg-proxy-printer".