Mac Mini not booting correctly after update to 10.14.5

I have a new Mac Mini which came with OS X 10.14 Mojave installed. After updating to Mojave 10.14.5 the system is not booting correctly.

1. No startup sound
2. The Apple Logo appears, but, when the progress bar is halfway across, the screen goes blank, and the system is unresponsive.
3. I am unable to boot into Safe or Recovery mode, or to reset NVRAM/PRAM or SMC, as the Mac always tries to boot normally.
4. If I turn off by holding down the power button, and restart holding down the Cmd button, the screen will blank as before, but on most occasions the screen display will recover, boot will complete, and I can log in.
5. I use a Logitech wireless keyboard, but I do not see that should be an issue, especially as I had no problems with 10.14.4.
6. Neither EtreCheck nor MalwareBytes reveal any issues.

Does anyone else have a similar problem? But more important is there a workaround until Apple sorts out the problems with Mojave?