Here's how to build it from start to finish (assuming you are running as root on a TKLDev):

cd products
rm -rf bookstack # in case it already exists
git clone https://github.com/JedMeister/bookstack.git
cd bookstack
make

When run, it should always install the latest release (it clones the HEAD (latest commit) of the Bookstack release branch.

Now that Debian Bullseye has been released, hopefully it won't take too long to get an RC of v17.0 built (I'll pubish Core and TKLDev once we have them). Once I'm comfortable with the LAMP appliance, I'll aim to make this an official TurnKey appliance. Not sure how long all that will take, but if you keep an eye out for the RC announcement, helping test that would certainly help things move along...