The following PyQt5 classes may be pickled.
QByteArray
QColor
QDate
QDateTime
QKeySequence
QLine
QLineF
QPoint
QPointF
QPolygon
QRect
QRectF
QSize
QSizeF
QTime
Also all named enums (PyQt5.QtCore.Qt.Key for example) may be pickled.
The PyQt5 Resource System
Using PyQt5 from the Python Shell