SingleWebPartAppPage not working in MS Teams Desktop Client

Hi Srinivas Narula ,

One thing you can try is adding another "supportedHost":

TeamsTab

(See example on https://docs.microsoft.com/en-us/sharepoint/dev/spfx/web-parts/single-part-app-pages). 

I don't know if this will solve you issue though, it's just something you might try.

I have a question though, if you are using a SingleWebPartAppPage, isn't it more interesting to directly add the webpart as a team tab instead of wrapping it by a page and adding the page?

More information about this can be found at following location:

https://docs.microsoft.com/en-us/sharepoint/dev/spfx/web-parts/get-started/using-web-part-as-ms-teams-tab

Hope this helps!