So far i know there is no quick button/setting to auto create reference curves when creating lines in a sketch.
What you can do is after you created the curves use the feature "Convert To/From Reference"
In this feature you are able to select multiple curves and convert time in 1 time to reference curves.
"Very often a sketch is mainly composed of reference objects."
Not true for everyone; in fact, you may be in the minority on this point.
Hi @TimF Thanks! Often in my sketches, there may be 5 general curves/points and 20 reference curves/points. With Ctrl-A I would still need to deselect those curves/points not for conversion to reference.