Hi @600toogood
It's a great question. Power Apps Portal is backed by DataVerse. The license you are paying includes dataverse. The screenshot, you have provided, will only show the list when you create a table in dataverse environment.
If you feel, that your company employees are comfortable in using Microsoft list. (Part of office 365 license), then here are the steps for you.
You can achieve this by Dataflows. Adding an official link below to go through.
https://docs.microsoft.com/en-us/powerapps/maker/data-platform/create-and-use-dataflows
I have tested this and it is working fine.
Steps:
1. Create a data flow and make sure you select "SharePoint online Services" as the source
2. Once your Microsoft list is ready, copy the URL up to the site name. Example below

Example: https://yourdomain.sharepoint.com/sites/sitename/
Note: this step is important remove your lists/listname
3. Create a data flow and choose SharePoint online as source like below and pick the list you want to connect

4. Import the data and load it to the new table

5. Make it an Automatic refresh depending on your need.
6. Once connected, you can see your list's data in the dataverse environment.
7. Then create a list in portal management or portal studio and connect to the data
Note: There is an active bug in Datalfows reported by many users recently, the dataflow is not set up properly at this stage. you may need to raise a support ticket with Microsoft if you experience any issues.
Hope it helps.
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