[GNC] report of investment income and capital gains (realized and unrealized) for the previous year

[rsbrux]

The Advanced Portfolio is close to what I want, but gives me the
numbers over the entire time I have owned the securities.
Is there some way I can modify the report to show the *difference*
between the end of year results for two consecutive years?
If this requires learning scheme, I would appreciate being referred to
a good tutorial (preferably a document, not a video).
I found some useful info here:
https://gnucash.org/docs/v5/C/gnucash-manual/report-create.html
but am surprised that no one else has addressed this, as I imagine it
would be needed for tax reporting.