Merge cells from different Excel Workbooks

Ideally the cells that you're interested in would be named ranges (see more here:
https://support.microsoft.com/en-us/office/create-a-named-range-from-selected-cells-in-a-worksheet-fd8905ed-1130-4cca-9bb0-ad02b7e594fd)

when connecting to such Excel Power Query will recognize the ranges the same way it recognizes data tables and sheets

Otherwise, if the structure is static you would need to create a logic to get to the specific cell from the messy input, but that's a bit ugly solution.

As for the multiple files, you can connect to folder (remember to exclude subfolders if needed), and use single extraction logic for all of them