Third-party software to enable qt to play midi files through installed devices as it used to do, or even anything you choose, like vst? Since qt 6? 7? this hasn't worked. Only plays back through the hideous built-in sounds, or cheesy sound fonts sf2. Super-irritating, as this used to be easy & worked great. Seems like the whole apple midi thing is poor. Maybe no one else uses it anymore, but I do--I'm a pianist; & use midi to easily record my playing.
Well, audio midi setup has zero to do with the quicktime player's inability to playback midi files except through the useless built-in sounds, or sf2 soundfonts, as far as I can tell. There's no option for "other synthesizer", as there used to be.