It’s been a few years since I used SketchUp with any regularity. I had a computer failure and it was several years before I got another computer that could run SU. Now that I have a capable computer and SU again, I find that I have lost some of my knowledge.
I seem to recall that it is possible to select geometry and replicate it using the mouse and a keyboard key, eg, alt, ctl, shift ? Am I having a senior moment?
On a Mac, select the geometry with the mouse, press m, press alt then move the copy with the mouse, or select geometry, press m and move to desired location then press alt before clicking for end of move.