I’m using an old 2014 Mac mini which still manages to work pretty well on Monterey. It has the more powerful i5 CPU @ 2.60GHz paired with 8GB of soldered RAM and a 1TB SSD that I replaced by myself.
What do I use it for? Well, to be honest I’m increasingly using my iPad Pro for many of the tasks I performed on the Mac mini, mostly text editing, PDF reading, web browsing and email. Those are more conveniently done now on my M2 iPad Pro.
But I still use it for playing, every once in a while, using GeForce Now (there’s no native app for iPad), and some tasks that cannot be done on an iPad like managing torrent files download.
What I’m really eager to have an M4 Mac mini for in the future, is to be able to compress big video files with handbrake, which sadly isn’t available for my iPad.
The 2018 Mac mini allowed you to expand the RAM by opening the device. It was an exception unfortunately, as they reverted back to the soldered RAM modules (this time on the M1 SoC), with the 2020 Mac mini.