new graph, select export graph or export graph (advanced)
select follow dark mode colors, ok
new another graph, select send graphs to pdf from app bar (install Send Graphs to PDF app)
select a pdf path for save file as option, ok
open the pdf ==> graph use dark mode color. After step 2, Dark Mode: Copy as displayed, excluding background auto color in Preference: Options dialog Page tab is selected. For export tools that do not provide follow dark mode colors checkbox, they will just follow settings in Preference: Options dialog.