NetNewsWire 6.1 was just released and it includes a hidden preference just for me (but you can use it too)!

To turn off the feed pull that happens on start up:

defaults write com.ranchero.NetNewsWire-Evergreen DevroeSuppressSyncOnLaunch -bool true

@cdevroe I don't know what netnewswire is.. but my rabbit hole senses are tingling.