Hi @Kevin Thankachan ,
Per my test, I got the same results as yours on my end.Looks like we cannot publish the app through App Studio, the app studio is to test custom apps.
To publish the app, you could download the app package and upload the app package to your organization's app store. You could refer to this: https://learn.microsoft.com/en-us/MicrosoftTeams/manage-apps?toc=%2Fmicrosoftteams%2Fplatform%2Ftoc.json&bc=%2FMicrosoftTeams%2Fbreadcrumb%2Ftoc.json
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