HestiaPi Touch raspbian image build

Is there any documentation on how HestiaPi Touch’s OS image is built? The version shipped with my unit is still on Raspbian Jesse. I’d like to upgrade this to Buster and apply some extra customizations to the image.

I believe there are limitations with the software used that does not (yet?) work with Buster. Beyond that @HestiaPi will have to answer.

The process to “build” the image is pretty manual installing and configuring all software then clearing settings, logs and WiFi details. Finally image is written to disk, removing empty space to shrink as much as possible.
As far as OS goes… we depend on the LCD drivers to support a method to be used from a CLI environment to launch the LCD UI in a browser window in kiosk mode (no: window decorations, menu, toolbar, address, warnings or popups). We tried our first go on this but got stuck. Need to restart this as Jessie is ancient now.