I am happy to report that I have had success in getting my PC working again! On another computer I downloaded the Windows 10 May 2020 Update from the Microsoft website onto a flash drive following all the instructions for installing it on a different computer.
On our slow internet this took several hours, so be patient. I powered up the problem PC after plugging in the flash drive. The computer opened to what I believe is called the Windows RE screen. Choose the Troubleshoot option and then select Repair (the repair
statement is smaller at the bottom of the page). Very quickly I had my login screen back and after logging in found that all data was intact.
After the computer was running, the notifications icon was highlighted and on opening it said that Microsoft had deleted some updates that had caused a problem with the computer starting. I checked the Microsoft updates history and saw that the problem scsi
download was shown as "Failed." I am not sure if the failure was the original attempt to install or reflected that Microsoft had deleted it.
I hope this may be useful for others with this problem. And, pausing updates for a while is probably still a good idea!