Man pages matching name qwtplotlayout in section 3:

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