Moreover, PowerApps doesn’t support columns that support multiple values or selections.

  • For Lookup columns, the Allow multiple values checkbox must be cleared.
    Check box to allow multiple values in a Lookup column
  • For Managed Metadata columns, the Allow multiple values checkbox must be cleared.
    Check box to allow multiple values in a Managed Metadata column
  • For Person or Group columns, the No option under Allow multiple selections must be selected.
    Options to allow multiple selections for a Person or Group column
  • For Choice columns, the Drop-Down Menu or Radio Buttons option under Display choices using must be selected.
    Options to display choices for a Choice column

Source: https://powerapps.microsoft.com/en-us/tutorials/connection-sharepoint-online/#known-issues