What is the best way to create a Team SideBar PowerApp ?

Hello,
I have a confusion around PowerApps for Teams.
I found two ways of creating PowerApps but can't see why and how they are different.

My goal is to create an app that appears as a sidebar app in teams meetings, showing online team members where each of them can click a button to interact with it.

I first connected to https://make.powerapps.com/ and made a first app, I changed its settings to allow it to be a sidebar app but I wasn't able to publish the app because on constraints in my environment.

I was told by administrators here to create an O365 test environment where I can have a special instance of Office and Teams and make my app there as a test lab.

Which I did, I opened https://www.office.com/, clicked on Teams and from Teams, openned Power Apps and created an app from there.

This app, does connect to the test Teams, I'm able to list the meeting participants but can't configure the app as a sidebar as I don't see a download package button.

What are the differences between the apps created using each of those methods ?
Am I going in the wrong direction ?

Thanks for any help