The chassis and the port selection are essentially the same from the UM780 XTX model that introduced an OCulink port and a larger cooling system for up to 70 W TDP over the initial UM790 Pro. However, the UM880 Pro is powered by the Ryzen 7 8845HS and the UM890 Pro gets the more powerful Ryzen 9 8945HS.https://www.notebookcheck.net/Minisforum-launches-UM880-UM890-Pro-mini-PCs-with-AMD-Hawk-Point-APUs.847380.0.html
Main difference is better AI co-processor (which is useless for 99.9% of people), and RAM should be slightly more stable.
Other than that... HX 370 should bring a much higher improvement, but who knows when AMD will start actually selling them (it might take a year or so, hopefully earlier).