Please correct me if I'm wrong. I'm working with an Electrum Server, so I look at a bunch of traces of different wallets talking with the server. That's my main source of info (except for mutiny, which uses Esplora. That one I've looked at the rust code)
Discussion
One thing that popped to mind about sparrow: I'm using a "private Electrum Server", so maybe they do check for public nodes.
