With a few inexpensive upgrades (ram and SSD), this early 2009 mac mini runs Mojave surprisingly well : r/mac
Here are the Macs that will work with MacOS Mojave - CNET
OSXWiFi Mac Pro 2009 802.11 A/B/G/N/AC with Bluetooth 4.2 macOS Mojave Catalina 5,1 - Handoff and Continuity Broadcom BCM943602CDP 10.10+ Upgrade Kit and Mac Pro 2010-2012 4,1 Network Cards avenueeventgroup.com