The only two custom gamemodes I've tried are Clockwork and Nutscript so there may be some gamemodes where you can connect with an iMac successfully. However, if you connect with an iMac to any server using Clockwork or NutScript you crash after the Sending Client Info stage. I talked to Kilburn and he mentioned that it was likely a bug with Garry's Mod's support for iMac. I want to note that I can successfully connect on my Macbook Air, so it's not an issue applying to all Mac devices.
The only two custom gamemodes I've tried are Clockwork and Nutscript so there may be some gamemodes where you can connect with an iMac successfully. However, if you connect with an iMac to any server using Clockwork or NutScript you crash after the Sending Client Info stage. I talked to Kilburn and he mentioned that it was likely a bug with Garry's Mod's support for iMac. I want to note that I can successfully connect on my Macbook Air, so it's not an issue applying to all Mac devices.