How to copy folders with merging in Mac OS?

Question

macOS

When copying folders, sometimes a Mac gives you the opportunity to copy a folder to an external drive with merging, while replacing old files with new ones, adding new folders but not deleting old folders and files.
But for some reason, the Mac does not always give such an opportunity ... Is it possible to somehow forcefully copy folders in the merge mode, and not by replacing?

Answer 1

hold Option while dragging, select the Merge option in the dialog