I work in Swiss banking. We also have such a system for payments. Its very popular and used by most people. I keep saying they should use it as SSO, if you can authenticate payments you damn well can authenticate login requests. It makes no sense to go to an online shop, log-in with your shop account or google, and then when you pay, authenticate the payment with TWINT. And banks could even use it to login to their e-banking. Currently literally every bank has its own 'Access' App, that is almost the same but slightly different. And to my irritatingly they don't consistently encode TWINT information the same way into the normal banking transactions.
Our developer phones have like 40 apps on them to log into different test system, its madding.
In our system the pay system is also 'half' branded so you have to download 'TWINT-<bank>' not just 'TWINT'. Making it unnecessarily confusing and its literally the same app (from a user perspective).
It seems this Bank Id is an even earlier system adopted for modern SSO use-case.