Why did you change how it works right here?

I find it confusing to call the pattern "regExp" and the QRegExp object "m_myRegExp".

Then call it m_regularExpression?

Another point (which I forgot since it has been some time since I last looked at this patch), QRegExp stores the match info in itself, whereas QRegularExpression stores the match info in a QRegularExpressionMatch object (returned from calling QRegularExpression::match()), so if I use a m_regularExpression I'll have to add a getter for it, so that it can be called from URLGrabber::matchingActions().

Then you want to store a match?

The code stores the QRegularExpression::capturedTexts(), m_regexCapturedTexts, which is eventually what ClipCommandProcess uses.

What is silly about it?

The original code in ClipCommandProcess used:
const QStringList matches = action.regExpMatches();
which was:
QStringList regExpMatches() const { return m_myRegExp.capturedTexts(); }