A 2011 iMac runs horribly with out-of-date MacOS but great with Debian Stable.

Now that I’m running a new Debian 10 Buster laptop and use Dropbox to sync 160 GB of personal files, I have turned to the open-source, Go-coded Syncthing to keep about 500 MB of work-related files mirrored across that Linux laptop, a Windows 7 desktop and a 2011-era iMac desktop. It’s all pretty much seamless. I have the Syncthing client running on each PC, and I can monitor the “state” of the sync via a web GUI.