On my first version 2018 supplied on a HD I just created a BiaB 2018 folder on my external SSD and copied everything from the original BiaB HD in that folder. I opened the app from the SSD, added it to the dock and have had no problems at all. All the updates were installed later on the SSD and have worked right off.

MacBook Pro 2020 - Big Sur 11.2.3
BiaB UltraPak+ 2020 Mac, (423)
Yamaha SLG200N
Epiphone Les Paul Studio

Logic Pro X,
Xtra Styles 1 - 10. Loops-with-Style PAK 1 & 2. Multistyles PAK 1.