I work with several software packages (AutoCAD/Rhino/Sketchup/Blender) that all have "Mirror along line" capabilities or use plugins that do. I live by it.
Though I haven't been using Corel as much as I used to, I'm currently back using it. (2018) I seem to remember at some point I had a script or plugin that gave me mirror on line capabilities. Perhaps CADTools 5? Or maybe it was a how to video. Any suggestions?
I skipped v2018, but I think the new Symmetry feature may be what you're looking for?