When you create a Power Apps app for Microsoft Teams using Microsoft Dataverse for Teams, the app needs to be added to the app bar in Teams before it can be accessed by users. This can only be done by a tenant administrator. To ensure that users can access the app, you would need to request that the tenant administrator pin the app to the app bar in Teams.
Sharing the app with a security group by using the Maker portal (A) or in Teams (B) would allow users in that group to access the app, but they would still need to be able to find and open the app.
Here are some references from Microsoft that may be helpful in understanding how to make Power Apps app available in Teams:
* Microsoft docs: Add a Power Apps app to a Microsoft Teams channel
* Microsoft docs: Pin a Power Apps app to the app bar in Microsoft Teams
* Microsoft docs: Distribute Power Apps for Microsoft Teams