Apparently, at least on my system (OS 12.0.1), the 1.8.8 update did not fix the problem. I have attached the crash log.
Whoops. BibDesk Version 1.8.7 (5747)
I have perfect reproducibility on my MacBook Pro (16-inch, 2019), Big Sur v11.5.2. Every time I quit I get the crash log coming up, I have attached it.