The new Microsoft Teams Desktop client was made generally available for Windows and Mac recently. The good news is that the new client provides feature parity for 3rd party apps like Focusworks AI giving customers a choice of using their preferred Teams client to access the apps.
However, if you have a custom built Microsoft Teams tab or a task module as part of your solution, and find that it fails to load in the new Microsoft Teams client, there might be a specific reason for it.
And since there is no way to invoke the Developer tools in the new Teams desktop client yet (November 2023), the experience can get a bit frustrating.
In my case, I have a custom React/TypeScript based tab which is using the @microsoft/teams-js library to interact with Teams.
Since teams tabs are just HTML pages, we need to make sure that the page is being loaded inside Teams before continuing to execute the code. To do that we can use the context.app.host.name property and check that the value was "teams" before moving ahead.
However, with the new desktop client my tab was failing to load. After a bit of digging around I realised that the new Teams desktop client has an entirely different host name property and the value is "teamsModern" as mentioned here: https://learn.microsoft.com/en-us/javascript/api/%40microsoft/teams-js/hostname?view=msteams-client-js-latest
So changing my code to include the new value as well worked!
Hope this saves you some debugging time!