Here’s the HP manual: http://h10032.www1.hp.com/ctg/Manual/c03351672
Your options here are VGA or DVI. Limited. Low-res.
(Also not HDCP. No protected media content with this monitor. But that’s not the central issue here.)
Here are the Apple configuration details:
Connect a display to Mac mini - Apple Support
This will involve the USB-C VGA Multiport adapter, or the USB-C to DVI adapter.
Check the adapter to see what resolutions it supports.
You’re likely running into issues with the the adapter or the cable, maybe with the monitor settings.
This monitor is… pretty limited. Any digital TV will have higher resolution, have HDCP, and HDMI connections.