Export my bib to spreadsheet with custom fields in bin entries like impact factor and include DOI and ISSN

Here comes the feature description…
When I export to spreadsheet it drops all my custom fields as well as it strips ISSN DOI while exporting
I have few custom fields in bib entries as impactfactor, index, issn, proof url


impactfactor={impactfactor of journal},
index={whether indexed in WoS, Scopus, IEEE etc},
proof={master journal list URL or Scopus source URL}

I import this in jabref and added these keys is shows in the window,
but when I export all entries, the exported spreadsheet do not have any custom field and ISSN and DOI fields are also missing.


This is already possible. You just need to add them to the layout files:

You can find the layout for csv files here