I would like to sync only when manually run Syncthing. When I cleared RAM/killed app, the Syncthing still running in background. I need to “Force stop” Syncthing manually.
When you have the “Always run in background” option disabled, you can stop Syncthing in the side menu of the app. This will stop the background service and quit the app.
I don’t know what you mean with “When I cleared RAM/killed app”, as the only way to kill tan app I know is to force stop it in the android settings, I can’t say why that didn’t work. But probably, because the Syncthing binary itself is run as a separate service, which is controlled by the app, so your means of killing the app probably just killed the app, not the background service.