Insert scope change [Dorico 4.0.10 on Windows] via mouse only with a very short mouse click possible

I think the two of you are talking at cross purposes. @Michael.B is talking about this issue:

This is not solved in Dorico 4.0.10, but we have since made some further fixes that I believe sort this out – our QA department are currently looking at the fixes. If all is well, those fixes will be included in the next Dorico 4 update, expected at the end of February (though these dates are subject to change).