If you’re seeing the banner, then it means that your browser is missing support for one of these three features:
If you open the developer console, you should see a red message which includes true/false values for each of these.
Our headline here is “iOS 15”, because that’s the most commonly-used browser that is missing these features. But the change also applies to other browsers which are missing the same features.
Unfortunately, it looks like Kiwi has been officially discontinued 