I have Syncthing v1.20.3, Linux (64-bit Intel/AMD) qpkg installed from QNAPClub. The installation directory is /share/CACHEDEV1_DATA/.qpkg/SyncThing, and it appears that there are many files there besides those that need to be backed up to save the configuration.
Ideally, I’d like to store the configuration separately in a different directory. The documentation refers to --home, --config, and --data options.
How do I run these commands on the QNAP?
What is the procedure for restoring the saved configuration?
With the exception of the Android app, there’s no built-in method to back up and restore Syncthing configuration. You just need to copy the files, e.g. manually, and then restore them the same way when needed. I’d strongly advise to check https://docs.syncthing.net/users/config.html first and make sure which files you actually want to back up, as for a full backup, you do need to have almost all the files that are stored there (including certificates, database, etc.). The absolute essentials are the config file itself and the key files though.
As for the commands, you probably can’t run them easily when using a 3rd party package like that. Please also remember that even if you do manage to run them somehow, you still need to move the files from the original location first, as Syncthing won’t do it automatically, and it will rather just create a new config instead.
If you want full control over Syncthing, I’d guess you probably need to use just the binary instead of the package that the OS provides, if that’s even possible, of course.
This causes the configuration and database files to be stored in the installation directory. Changing this command in the .qpkg file is inconvenient, so I’ve just configured my backup system to selectively back up the files documented in the link you provided.