Hi,
Am unable to open the xaml files included in the folders of the program as shown below,as the studio got updated today!!
From the 2018.3 onwards, you should open .json files to access your project rather than the Main.xaml file.
If there is no .json file generated for your project, you can manually go to the folder with your file and open the Main.xaml file by double clicking it. It will generate a .json file in the same folder and you will be able to open that .json file in Studio 
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Ok @loginerror, thanks!!