I (accidentally) applied the update to my High Sierra install to 10.13.6. NVidia popup asked if I wanted to update the NVidia drivers, and I did (since the screen was wigging out until I did so), and that worked great. But USB 3.0 was not working. In trying to diagnose/fix that, I
heard I needed to update the AptioMemoryFix-64.efi, and in order to do that, I tried using the Clover Configurator. That offered to update Clover to 4934. After doing that, the Clover bootloader comes up, but booting to anything results in a black screen. With -v boot option, I saw that I was stuck at "End Randomseed ++++++".
So I dusted off my USB thumb drive installer, used F12 to get to the boot menu, selected the cryptic "UEFI: General UDisk 5.00, Partition 1", which booted with an older Clover (4297) that still works. Then I used Clover Configurator (on my USB stick) to mount the EFI partition (the one on my main boot hard drive, which was notated with a bunch of boot-like things that all the other hard drives' EFI partition lacked). Then I copied /usr/standalone/i386/apfs.efi to /Volumes/EFI/EFI/CLOVER/drivers64UEFI/, because someone said that would help. But that didn't fix the boot problem (but hopefully didn't hurt anything).
Finally, while there, I went to the "Install Drivers" section of Clover Configurator and selected "AptioMemoryFix-64.efi", downloaded and installed that, and then rebooted (using the new clover version, 4934), and it all came up working great. Whew.