What does it mean when a process is surrounded by parens in `ps`?
When you see a process in parentheses/brackets it means that ps could not determine its command (which appear in the CMD column). This might explain why you don't see it in the Activity Monitor.

You can restart Finder also outside a shell. Just click on the Apple symbol in the top left corner of the MacOS task bar, click on Force Quit and select Finder (usually at the bottom)

Generally, I find top more convenient than ps, but I think both should work equally fine.