@Stormice @astoneham
What are your OS versions are your macs?
Apple icon (top left) > About My Mac
Warcraft III Classic (which is reforged now), requires you to be on OS 10.13 (latest patch) minimum or even the current OS 10.15 (latest patch) recommend. Do note, this is due to the fact that the game has been updated for more modern macs that make use of the Metal API. The game is no longer backwards compatible with older Mac OS.
Details on requirements are at the following link:
https://us.forums.blizzard.com/en/warcraft3/t/warcraft-iii-reforged-system-specifications/13881
Hopefully that helps, and note that OpenGL will not work anymore for more current patches of WCIII. Patch 1.31 and below are the only patches that support using OpenGL and thus older macs.