The issue is then the manual trigger maybe, if the flow is triggered by X then it will only pull X's items. How is the SharePoint list setup, do you have only allowed to view/edit your own items?
If the owner of the flow has a manual trigger as test, the same owner of the flow is an owner of the SP site and can read/write all items, then I don't know why it would only pull items related to that user.
But with manual trigger this sounds like it should work actually, i used this alot myself, pulling all items sorting etc