1. Monobank != Ukraine bank

2. Monobank[0] IS "internet bank"/subdivision of real ukrainian Universal Bank[1] that since 2017 bought and operated by TAS Group[2], affiliated with ukrainian oligarch Sergiy Tigipko[3].

[0] http://uk.wikipedia.org/wiki/Monobank

[1] https://uk.wikipedia.org/wiki/%D0%A3%D0%BD%D1%96%D0%B2%D0%B5...

[2] https://uk.wikipedia.org/wiki/%D0%93%D1%80%D1%83%D0%BF%D0%B0...

[3] https://uk.wikipedia.org/wiki/%D0%A2%D1%96%D0%B3%D1%96%D0%BF...

So in other words it is a Ukraine bank, just like the title says...

No, it's NOT a bank in any way.

>People who manage the 10,000 steps are granted a rate of 21% on their savings. Anyone who fails to walk the walk for three days in a row will see their rate slump to 11%.

Does anybody actually expect to get the money when they decide to cash out ?

21% is not an insane interest rate for UAH. Normal market rate is currently around 19%.

Is is currently 17%, not 21% (dropping to 15% if conditions are not met) according to what I see in Monobank app.

I don't understand how the bank can afford to pay out a 21% interest rate.

Probably because local currency. Different currencies have different inflation rates.