Just verifying... Have you scrolled down in the Add a Tab dialog? I didn't see PowerApps until I scrolled...
Also, if you're using the Teams desktop client, you'd want to make sure it's been updated: https://sandyu.com/2017/04/06/teams-get-version-updates-for-the-client-app/
Does this help you...?
Hmm, I'm afraid I don't know the answer to that, sorry. I have an E3 tenant with Early Release turned on, but in the MS blog post about this feature, they don't mention any particular license requirement: https://powerapps.microsoft.com/en-us/blog/powerapps-teams/
I see that a couple people commented on that blog post that they couldn't see PowerApps when adding a tab in Teams, but that was a few weeks ago, and I don't see whether they got a final resolution to that... Maybe you could add a comment there as well?
There is a problem between the web version and the desktop version -
My desktop version only shows Excel, PowerPoint, Planner, Word, OneNote, SharePoint, PowerBI, PDF, Stream, Website, VisStudio and Wiki.
In the web version I get everythnig. I've installed a powerapp tab on my web version which works fine, but the tab does not display in the desktop version.
I have Microsoft Teams Version 1.0.00.16451 (64 bit). It was last updated on 28/06/2017.
Edit: It has corrected itself now. Did a full log out / shut down of teams after checking for update. It appeared after logging back in.
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