Initially I had a bad Xcode to 11.4 update which I got resolved by reinstalling Xcode. Then I found that Items are not selected and GestureRecognizer was not firing Tap events in my apps. Then found that it is same even with the built-in TabbedPage app. But ToolbarItems are firing Click events. Once I go to a ContentPage from ToolbarItems there is no problem.
Created another blank project with just a ContentPage and Click events are firing.
Same issue whether I run apps from VS on Windows or Mac. I even reinstalled VS for Mac 2019 but in vain.
Windows 10 - 1909, Mac OS Catalina 10.15.4
VS on Windows 2019 Enterprise Ver 16.5.2
VS for Mac 2019 Enterprise Ver 8.5.1 (build 42)
Mono 22.214.171.124 (This was 126.96.36.199 when tried from VS on Windows)
Xamarin.iOS Ver 188.8.131.52