Great job of laying out what you want and are doing :-) (no sarcasm intended I mean it).
To best figure this out we need a couple of things
Let's do the simple questions first harder ones next
1) can you please share a Flow Run, where you have your Apply to each, where it runs through the Rows of data in Dataverse and then outputs it to your Table in Excel. I'd like to see the actual output of the List Rows to make sure we are getting data
2) can you please verify for us, does the excel file already have the table, or are you dynamically generating the table and then using the item { } propery to define the values of a row?
3) can you show us the key value, table structure, row structure etc.
Either the data is actually NOT getting out of Dataverse or, you are not actually writing it correctly, or there is a caching issue where the file is not ready, or the Table is not valid.
If you can literally take screen shots (and paste them in, don't attach them) or put a URL video link so we can see the actual flow run, that was called from Power Apps so we can validate that the data was pulled properly from Dataverse and iterated through properly, then we can make sure that the Actions you are using to write the data are correct, so the flow would be nice too.
If these suggestions help resolve your issue, Please consider Marking the answer as such and also maybe a like.
Thank you!
Sincerely, Michael Gernaey