Banking apps come to mind.

This is the only reason my phone's not running Lineage. I need those apps mainly for 2fa (some banks don't give me any alternative) or for one or two with no web app.

It feels like a total artificial duopoly, you only get to use your essential service on android or ios.

No other "real FOSS Android" is going to pass SafetyNet either, though

what would a banking app do that a bank website can't, exactly?

Many bank websites require bank apps or hardware tokens to login.

IIRC some finance apps either don't have web sites that can perform financial transaction, or are lacking a number of features of the mobile app. Cash App and Venmo used to be some of the worst offenders, but have improved in recent times.