

Sideloading is simply a matter of installing an APK file onto your phone. Where that APK file comes from does not matter.
If Google bans the banking apps I cannot imagine that the banks will just accept and tolerate that without a fight. They would be the ones likely distributing their own app
“Go to Rabobank.nl, and download our Rabobank app”












Because people expect their app to be on the app store, and the app store is still available?
Sideloading is more of a pain for the average user compared to just downloading it from the app store, and as long as it isn’t necessary there is not much reason for banks to accomodate it. However, that doesn’t mean that once it becomes a necessity, it’s impossible to set up methods involving sideloading to get around restrictions from Google.
Edit: As an example, the Chinese have Android phones, but the Google Play Store is not available in China. They have different app stores to “sideload” applications onto their phones. In theory they could also install APKs, if that is how apps would be provided to them.