Hi,
This seems to be VST Instrument Racks only. As a test, I just created 65 Instrument Tracks (Mystic), which was allowed. Then I add 2 more VST Instrument Racks. So I had 67 instruments.
Then I added more and more Instrument Racks up to 64. Then I wasn’t able to add more Instrument Racks. But I was able to add more Instrument Tracks. So at the end, I had 130 instruments. There is unlimited count of Instrument Tracks, as descibed.