You will ideally need an audio interface if you aim to have some decent results. Sky is the limit, but you may look for some as low as $200 or less if used.
you did not mention which mini you have. Older (like 2018) have thunderbolt, usb-c and usb3 ports. Newer have only TB/usb-C so choice of the interface will depend on it.
Typical interface will allow to connect to external monitors and headphones. With it, you eill also be able to record real instruments, microphones, and of course, playback softsynths. Some may have MIDI connectors for keyboard/controller.
Some low-end (yet excellent) interfaces: Focusrite, Steinberg/Yamaha.
Make sure the unit you chose if compatible with the macOS version you are using.