Maybe my post was a bit convoluted trying to cover all angles.
It does work with Studio One 5 fine as I have been using it on both the Mac M1 and the Windows 10 laptop for over 5 months now without any problems.
My gut feeling is that your MG2 input track is not routed correctly to the instrument, after diner I will check out how I have routed the MIDI Guitar 2 input to the instument tracks, I have one song where I have several tracks set up for different instruments where I use MG2 as input and then activate the instruments that I wish to use either as a solo or layered sound.
So much for the diner once you go down that rabbit hole time is meaningless, a lightening strike blew my network out a while back and I have been using a usb drive to swap files between the PC’s as the NAS is on the Mac for Time Machine. I could not locate the files I wanted as I am doing a massive tidy up of drives so that they are all back in one place, the NAS drive.
Out of interest I have used my Sphere account to collaborate with myself between machines as that saves using the usb drive to swap the files until I get the new router, that is one of the reasons why I am so keen to use Studio One 6 as these features have been upgraded and I want to have a play before committing to collaborating with a friend in another country.
Okay I just set up a new blank song in Studio One 5 on the Mac M1 and this is the procedure I used to get it to work, again different to what I did before, but it worked. As mentioned before my MG2 plugin is installed as VST2 not AudioUnit.
You will have the track window now click on Mix and Browse down in the bottom right corner.
In the browser click instruments at the top and then navigate to Mojito or any other instrument then drag the icon across to the track window not the mixer window.
Above the track, top left you will see an ‘I’ just before the spanner icon, click this and an information panel will open for the instrument track and for me halfway down you will see In, Out and Channel, thus is where you choose what you need. I dragged over Mojito so Out and Channel say Mojito and the in is blank as no MG2 yet. If you have clicked Inst. on the left side of the mixer panel you will also see Mojito in the instruments panel on the left of the mixer window.
Now we want input so go to the browser and click effects at the top, navigate down to MG2 and drag the icon on to the track window, at this stage choose the input channel number for your guitar via your interface from either the track, information or mixer window, they all work the same. Click the loudspeaker icon to see the guitar working in the meter.
Now we have input to MG2 we can activate the input for the instrument Mojito by clicking on the instrument track and in the information panel go back down to the Out, In and Channel panel, In will probably say all inputs, change this to MIDI Guitar 2, again make sure that you highlight the speaker icon on the Instrument track as well.
Bingo you should naw hear Mojito triggered by MG2.
If you want to do A/B/C sound checks quickly just create more instrument track with MG2 as input and switch between them using the speaker icons, simple meerkat.
Hope you can follow that and given you something to work with until we get MG2 working with Studio One 6.