The Excel sheet needs to have a table. This is to help the app identify which column the data is located in. Once the table is identified, if you need to do more than just view the data (e.g. update, add, or delete), PowerApps will need to create a unique identifier column on the excel file, which is only possible if there is an existing table.
WORKAROUND IF CANNOT ADD A TABLE
Use PowerAutomate to import excel (make it in CSV format) to your desired data store (maybe an excel with existing table)
FUTURE CONSIDERATIONS:
If you plan to work with PowerApps long term, I recommend starting with SharePoint and eventually transitioning to a relational database like SQL or Dataverse. These options provide greater flexibility and consistency in how data is processed compared to storing data in Excel.
I hope this helps!
