Those pages are doing calculations in AL code to show the inventory by location, using tep tables, and in odata they don't display any data indeed.
Best is for example to use the Item page and the Item Ledger Entry page as odata or api data sources in Power BI. Then use the Quantity or Remaining Quantity fields of the Item Ledger entry table in combination with for example Location Code, to display in a Matrix visual or in Power BI measures.
Even better is creating Query (API) objects, Item, Item Ledger Entry,... with exactly the columns you need. Queries support group by, so the resultset is smaller and so the data load is faster in PBI.