store them in your password manager and pull via the CLI is a nice flow these days
you can store them in your password manager, but I found having to unlock that multiple times a day did not bring joy, so I just scp them between machines, and don’t store .ssh in my dotfiles repo
scp/rsync Documents. I hear Migration Assistant is good, but designed for initial set up. It can be slow if you’re on WiFi but there are tricks to speed it up if that’s going to be a problem