I use a cheap USB 3 hub on my mini 2018 for a year now without issue mainly because I don’t use wifi or bluetooth. Still on Mojave 10.14.6. The powered hub runs 2 ten tb drives, a mouse/keyboard switcher, and some other things. I have a Magic Trackpad 2 that I keep connected and a usb dell keyboard (does apple have a gray small usb/bluetooth keyboard yet?)Today, Nov 4th, is the day I decided to finally migrate from the iMac to the 2018 Mini. Hours of fighting with both bluetooth mouse and keyboard. The keyboard eventually behaved with a code to pair, but the mouse would connect and ide, connect and die, just as so many in this thread have described. I logged in to tell you that I had an Anker USB hub on the mini (it has too few USB A connectors when you're migrating from a 2011 iMac!). After looking through the comments here, I removed the hub and the mouse now stays connected.
Probably the first thing to do is REMOVE USB HUB from the mini. It must have been broadcasting interference.
Except, it disconnected again just now! But it's much better than before.