Thanks so much, so this project has about 40 tracks, but 20 are muted, now on this project because there are no drums, I've been recording at 48k, my previous album which I recorded and mixed was at 44.1k this had drums and lots of bells and whistles, (metaphorically speaking) with a lot more tracks per session and I did it with the OS High Sierra, with no problems.
Could it be the higher sample rate and not the Big Sur?