Question Mac Mini OS issue


Dec 9, 2011
Just VERY recently my fiancé's Mac Mini forced her to install a new version of the OS. She had been putting it off for a long time because she did not want to upgrade. It is an older Mac Mini. It forced an upgrade and now the Mac Mini is giving her a lot of issues and being sluggish.

About This Mac lists her stats as:

MacOS High Sierra ver 10.13.6
Mac Mini from 2011
Processor: 2.3 GHZ Intel Core i5
Memory: 8 GB 1333 MHZ DDR3
Startup Disk: Macintosh HD
Graphics: Intel HD Graphics 3000 512 MB

What should we do, please?