Hi @v-xida-msft
Let me detail you my issue here. I will begin by opening a new report. I'm currently on the September 2019 Desktop version:

Here's my current visualization pane:

I went to the marketplace to search for PowerApps and cannot find:

I go to the marketplace to search for PowerApps from this official link:
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/powerapps-custom-visual

Finally, maybe I deleted the visual on accident. Restore default and same result:

From here I'd like to share a few things:
1- I have a Pro license:
2- I am a Premium Capacity Administrator
3- I have previously and successfully built PowerApps into PowerBI PA visual
As a demo, I will use an older report which has PowerApps visual already installed (version 2.1.4). Here is the result and steps of my test today:
1- Navigate to make.powerapps.com
2- Create a blank canvas app from blank:

3- Save and publish.
4- Open PowerBI Desktop (with an older report which as PowerApps visual) and create a new PowerApps visual
5- Add in PowerApps Data:

6- Select "Choose App" and select the new app just created.
7- A new prompt will ask to save app in PoweApps Studio to save connection:

8- Check to see if PowerBI integration connection is available:

9- Yes, it's enabled. Using gallery test for field values. Set Gallery Items to PowerBIIntegration.Data:

10- Test for values from PowerBI Integration:



11- No fields found.
12- Save and publish to see if it even loaded into PowerBI PowerApps visual:

Demo 2: Open and Edit an existing PowerApps with PowerBI Integration:
1- Open PowerBI report with PowerApps visual already integrated
2- While inside PowerBI, edit PowerApps and navigate to PowerApps studio:

3- PowerApps studio opens with PowerBIIntegration connection:

4- Yes, it's still enabled. Check gallery Items property for PowerBI Integration:

5- No issues, look if there's any real connection between connection and PowerBI:

6- Gallery is empty. No information or values are shown whereas a few months ago it displayed information from PowerBI report.