Hi,
Technically its under ~/Library/Application Support/BeerSmith3 or you can use Go->Library and then nav from there from Finder.
The newer versions of BeerSmith also have a very handy File->Full Backup to Zip command which can be used to make a full backup but you probably need to complete your update first.
Also - check to see which OSX you have as there are two different downloads on the download page for Mac now - 3.2.7 is for Big Sur or higher and there is an alternate 3.2.7a for older Macs.
Brad