Man pages matching name qwtplotcurve in section 3:

QwtPlotCurve.3.en	debian 10 / libqwt-doc
QwtPlotCurve.3.en	debian 10 / libqwt5-doc
QwtPlotCurve.3.en	debian 11 / libqwt-doc
QwtPlotCurve.3.en	debian 12 / libqwt-doc