Another example of HS 2020-004 not installing correctly on mid-2010 iMac

[ERHiMac]

I too have this problem - every morning my mid-2010 27" iMac has a blank screen (black) with the cursor in the upper left corner after a daily early AM attempt to install 2020-004 update! In this state I can still move the cursor about, change the brightness & volume levels. I have nothing connected other than the Bluetooth keyboard and trackpad. I have checked the SSD from within MacOS recovery, all OK, reinstalled HS 10.13.6 (does this not include all recent updates??!?) but to no avail - still restarts to the initial conditions stated earlier with the 2020-004 update still required as indicated in the App Store/Updates section. The only way out is to power down and the power back on. I have tried doing the update whilst in Safe Mode and from a virgin new administrator account; also form a directly downloaded version from Apple support rather then that via App Store/Update. Otherwise all works absolutely fine!! I've even allowed over 24 hours for the update to potentially `work'. I have now run out of ideas, as well as hair!! Any other suggestions/clues appreciated. If push comes to shove, how can I disable this update completely such that I don't have to do a full power down/up every morning?