It has been awhile I’ve seen a corrupted firmware due to the Clover boot-loader.
Do you have access to a second Mac you can connect yours to using Target Disk Mode? Hopefully you can get your mini into TDM using a wired keyboard pressing the '''T''' key when your start your system. If not then the damage maybe to much that we can’t recover the systems EFI firmware (BIOS).
Reference:
* [https://support.apple.com/en-us/HT201255|Mac startup key combination]
* [https://computers.tutsplus.com/tutorials/understanding-the-applications-for-target-disk-mode--mac-60609|Understanding the Applications for Target Disk Mode]
If you can’t get to TDM then you’ll need to either replace the logic board or find someone with the skills and tools to re-burn your systems firmware.
Here’s one source for the logic board [https://www.thebookyard.com/parts-mac-mini-intel.php?cPath=96_400&sort=2a&filter_id=12|Late 2014 Mac Mini logic boards] and here’s the guide [guide|33077]