Mac Mini 2012 Late

Not only did the stock 2012 come with a rotational hard drive but it also came standard with 4GB of RAM which is basically what Catalina needs to run leaving little room for applications. The one nice thing about the 2012 mini is that it is pretty easy to work on. Head over to macsales.com and look at their installation videos to see what's involved in upgrading RAM and/or replacing the hard drive with an SSD. The typical reaction to someone who replaces their hard drive with an SSD is "feels like I bought a new computer!"

There were certain progressive upgrades to hardware required

to enable better quality of experience with these machines.

If yours still runs rotational hard drives, stock units are 5400-RPM.

Not sure these could even utilize Catalina installers; glacially slow.

Faster rotational HDDs, 7200/13000+ RPM do better; and solid state

drives are currently best for demands of newer, High Sierra forward.

There are several reasons why your Late 2012 Mac mini could be slow.

You may have to download and run EtreCheck to see what report says.

And post the report using tools in bottom of the reply you'd use here.

Issues and sources of condition status will show in there. Configuration

and/or resources available to your Mac are listed, too.