Some banks only provide access via apps (at least in the UK) so loosing access to the app also means you loose access to the bank account.

Ah. I've never come across this in the US - every bank I've seen also has a website. The only thing the apps do that the website won't is mobile check deposit typically.

Starling is an app-only bank.

They did indeed. I had to call customer services to get the account closed. The app being the only way to interact with the account, I was left without funds for days.