There are two sides of Xamarin. It builds native apps and you can use their native UI systems. So you can build a native Android UI and a native iOS UI next to each other. This will give you perfectly native apps with the ability to share as much code as possible.

The other side is Xamarin.Forms and its designated successor MAUI. Here you have the typical Microsoft UI problem. It is quite an unfinished framework. You can build everything with it, but if you do something else than the showcase app, you are going to have a difficult time.

Xamarin is for sure not going to die soon.