We've been working on our Xamarin Forms based product since the first beta in 2014. We released to Android first. Then in 2018 we built a UWP variant of our app. This process barely took a week if I don't include the technical debt that took an extra week to sort out. Then in 2019 we built an iOS variant of our app too - again barely taking a week to do so.

Xamarin Forms let us build 4 years worth of tech for Android only. And then, when we had time and the customer demand to do so, with a small amount of work - port our app to 2 other platforms in fairly short order.

I don't know of any other platform that could do this - particularly when considering the years involved.

Our app uses local databases on the device - so a web based app would not have cut it. And our app has roots in 2014 tech when many possible alternate approaches did not exist yet.