Solo Defeat on an External Instrument Track?

Cubase 9.5.21 - Windows:

Is there any way to activate “Solo Defeat” on an external instrument track? I send my MIDI synth’s audio to my mixer who’s outputs are sent to my audio interface. The mixer is defined as a Ext Inst in Cubase and it all works great. But when I solo a midi track it mutes that external instrument as well, which means I can’t hear the track I just soloed. It seems that one can only solo/mute the Ext instrument track in the Mix Console, which is fine. I can activate Solo Defeat (Ctrl-Alt-Click) on that track in the Mix console and that does turn the solo button orange. But even though the mute button does not turn yellow, that track still mutes when I solo another track.

Does anyone know of a solution to this problem? Your help is very much appreciated!