Earlier quoted context omitted.
When I started using a Mac many years ago, I also could not believe how terrible Finder is. This is software from the "design" company. One of the biggest pitfalls I ran into at the time (and remember from the top of my head) was that when you copy a folder, and a folder with the same name already exists at the destination, it will quietly replace it, rather than giving me a dialog asking if I want to Replace or Merg…
You can press Command-Shift-. (period) to toggle hidden files. This isn’t very discoverable, though. You can also hold Option while stopping a folder to get an additional Merge button, but at least one folder needs to have unique items.
But MacOS keyboard shortcuts have always been undiscoverable unless they were part of the menu, which is a problem.