Mac Mini 2018 - Display port connection to 4K monitor not working after update

Have just installed the 10.15.4 supplemental update and on restarting on the end my monitor never detected a signal again.

I had bought a USB-C to DisplayPort cable due to problems like this with other updates, or even sometimes after a restart, though previously the issue was persistent with HDMI only.

This time, DisplayPort has been 'taken out' by the update and I reconnected my HDMI cable and that now works?

3rd party monitor support with this Mac has been poor ever since I bought it. Never had so many recurring issues with Mac's in my life. Anyone else had this issue, any fix?

I've reset SMC and tried NVRAM reset (doesn't seem to work, the Mac just starts up normally).

The DisplayPort connection no longer gives a signal to the monitor, but HDMI does.