SoundSource is probably the easiest / cheapest (there is a free trial for SoundSource but there might be other freeware. I haven't looked into this in a while). It has a built-in 10 band EQ and support for AU plugins. It's useful for more than just EQ as well.

You can also use Loopback (more expensive than SoundSource) and route it through a DAW, standalone VST, etc.

There are also hardware solutions for this such as a DAC with DSP chips (Apollo Twin for example), and plenty of other ways via hardware.

There's also Roon which has built-in DSP functionality which includes an EQ though that would only apply to audio played through Roon.