Go to Edit>Preferences>Color. There should be a setting there to change the brightness of the game. If there is not, just click through all the options that seem like there could be a color correction piece. There is also a premade color correction script in unity. If you go into the main camera, then add component, and search “color correction” it should show up.
Otherwise, Mac is terrible at running games, so that might be a computer issue, and not a Unity issue.