As I understand, when a SharePoint Online list is integrated to use power apps. The default formula that is set for the ITEM property is:
If(IsBlank(SharePointIntegration.Selected) || IsEmpty(SharePointIntegration.Selected),First([@'YourListName']),SharePointIntegration.Selected)
This forces the Edit Form to open the First record in the list regardless of the item selected in the SharePoint list.
I have not located any solution that changes this to open the actual record that was selected in the SharePoint list.
Please note: I am not using Galleries or additional buttons on any Screen. We simply want the User to select the record they wish to edit and the Edit form opens for that record as it would if using the SharePoint lists default forms.
Also, once the Edit Form opens and is displaying the data of the first record in the list. If the users selects the 'Edit All' button located above the form. The form will refreshes and then show the correct data. However, this is confusing for end users.