It's all good now! I just booted Win10 with Shift, then I went to Advd ops/Start-up Repair (Fix problems that keep Windows from loading). Strangely it said it was not successful. Then I went to UEFI Firmware Settings, but when I clicked that choice it only had a Restart button available. It brings you to the BIOS. But once there, in the Boot Options tab, there was nothing that would allow me to turn off/on Fast Boot. Windows Boot Manager was nowhere in sight still. Then I restarted, and Grub showed up! Along with the Windows choices too. So I no longer need to boot from the rEFInd USB drive.
I will have to find out for the next time, where should I tell Ubuntu to install the booting files? Assuming Windows has been installed already, and I'm installing Ubuntu on a separate drive.