can't help with anything Mac but is the software MIDI Guitar (which I'll shorten to "MG" to save space/confusion) by Jam Orgins? [because I have/use that SW and can maybe help there].

First if Mac is like Windows then you probably can't use same near-realtime audio interface - so in MG in the "settings" whatever your Audio Device is I doubt both BIAB and MG can use it AT SAME time. That's a Mac thing - maybe you can maybe you can't I don't use Mac's.

Second a little further down in settings is the "MIDI output Route" this is where MG will send MIDI data to - for now I'll call it "internal MIDI 1" as you play the guitar.

Third BIAB's MIDI input (look under: "Options -> MIDI/Audio Drivers Setup -> MIDI input driver" needs to be looking to that "internal MIDI 1" device/port that you set in MG - (or in simple terms: output from MG NEEDS to go to input of BIAB)

Now that BIAB and MG are communicating (and not tripping over same Audio (sound making) device - BIAB can now record your MG MIDI in.

Remember recording MIDI will ONLY be recorded on either the BIAB Melody track or Soloist track.

Good Luck
Larry

Win10Pro,i9,64GB,2TBSSD+20TBHDDs,1080TI,BIAB'24,Scarlett18i8,Montage7,Fusion 8HD,QS8,Integra7,XV5080,QSR,SC-8850,SPLAT,FL21&others,Komp.14,IK suite&others, just a guitar player-AXE FX III &FM9T, FishmanTP, MIDIGuitar2, GK2/3'sw/GI20