When I payed a decent amount for logic express and 2-3 years later I couldn’t use it with the latest Apple OS.

Just gonna leave this here…

https://www.gnu.org/philosophy/free-sw.html

As I understand it Sync could charge for the app with a free software license, but wouldn’t be able to stop people copying or distributing it.

I don’t know if you mean on linux but in my experience I have found the bottom part of the first man page usually has a section on config file locations.