There is an app in the QNAP Club App Store. (You first need to add this to the AppCenter with the URL https://qnapclub.eu/en/repo.xml) But you could also download it from QNAP Club and install it manually, I suppose. Not via console, but via the AppCenter app on the QNAP Web-App. QNAP always executes installed apps with the admin user. Unfortunately you can’t change that. At least that’s what I found out. This means, that all files, that SyncThing creates, belong to the admin user. You can view them with other users, but you can’t modify them directly.