Can't get remote servers to sow in Mohave sidebar

I'm frustrated. I'm using a 2018 MacBook Pro (Retina and Touch Bar), and trying to get a remote Mac Pro (Late 2013, AKA trashcan) to show up in the Mac Book Pro's Finder sidebar. Both running Mojave 10.14.3, both on the same LAN, and with File Sharing enabled on both in the Privacy System Prefs and File Sharing and Screen Sharing and Remote Login ALL enabled in the Firewall.. This used to work just fine on my previous laptop (an an ancient 2009 MacBook Pro 17" running High Sierra. There MUST be a setting I'm missing, but I sure hope someone can point me in the right direction.