I revisited secushareBox (AKA boxen), built it from source and tried to experiment with it.
Sadly it didn’t want to print out any logs. Which is a problem, considering it was just silently failing. After improving the logging mechanism (logging into a file is no good if the user doesn’t know about the file!) I successfully went through the device initialization and installed the service onto my PinePhone.
Right after that I looked around the code some more and found out that there is nothing more. The tool is in a VERY early stage and all it does is the VPN service initialization. You’re on your own when it comes to actually using the service.