Mac:
The unsupported Heroes of Newerth Mac client is currently 32-bit. This means if you're running a version after Mojave on your Mac system you won't be able to play, since Apple dropped support for 32-bit applications. A 64-bit version of Heroes of Newerth Mac is currently in the works to support playing on Catalina and later, but it's not here yet.
If you're having trouble installing on Mojave or earlier versions of Mac, make sure you're first Allowing Third Party Applications to be installed.
-> System Preferences -> Security & Privacy -> General -> Enter PW and Unl