Sorry I misunderstood. I had no idea that Teams could be used to deploy software. I am just an ordinary-to-middling user of Teams, and know nothing about its superpowers.

If the Teams-based deployment is similar to the Intune-based deployment (I haven’t read the articles you linked to, and know virtually nothing about either), then I’ll say to you something similar to what I said a few minutes ago in another conversation: the regulars here aren’t necessarily experts in things like Intune or Teams administration; however, in this discussion, the user there showed an example script presumably used somehow in Intune to install Noteapad++ and some plugins; that script might be a starting point for you, depending on how similar the Intune and Teams procedures are.

What I understand is that an app can be uploaded by Teams Admin for the Org to use

This is the Teams instructions
Custom apps created within an organization for internal use
https://learn.microsoft.com/en-us/microsoftteams/deploy-apps-microsoft-teams-landing-page

Publish a custom app by uploading an app package
https://learn.microsoft.com/en-us/microsoftteams/upload-custom-apps

The page you linked to was about Microsoft Intune, which appears to be a system administrator tool to make it easy to distribute software to all the members of your organization (one of the many ways an IT team might build up a list of “approved apps” for their users). That post has nothing to do with Teams.

That article uses the word “deploy” in the normal IT sense, which means “to install on another machine”. I do not think that’s what you mean when you say “deploy Notepad++” (though I could be wrong). I think that you mean you want to associate .txt files to be edited with Notepad++ for yourself, and yourself only, when you come across a .txt file in Teams.

As far as any of my internet searches have said, you cannot edit .txt files in Teams (for example, this question which was answered by a “Microsoft Agent” says “For other Non-Office files ( like txt files) cannot be edit in the Teams.”)

And when I upload a text file to Teams, and click on the … button for that file, it doesn’t given me an Open In > submenu; it just gives an Open in browser option. That Open in browser just takes you to the web interface for teams/sharepoint, and edits the cloud version of the file there. But I don’t think Teams gives you an option to add an Open in some other application on my computer for .txt files (or anything else).

It may be that someone else here is enough of a Teams expert to show how this can be done (though if a “Microsoft Agent” says it cannot be done in an official answer on an official MS help forum, I am doubtful that it can be done). And if Teams isn’t capable of mapping file types to specific local-machine editors, then there is nothing that Notepad++ itself or the users who frequent this Community forum can do to add that option into Microsoft Teams.