KEGS is an Apple IIgs emulator for Mac, Linux, and Windows.
You must provide a ROM file (supports just about any known format, ROM01 or ROM03), and bootable image. The directions provide details on what you need.
Press F4 while it is running to change options.
KEGS is likely the fastest IIgs emulator, hitting over 1GHz on Mac M1 systems. It has many features, such as the ability to mount disk images directly from .zip files.
Binaries and other files are at: https://kegs.sourceforge.net/