Cant log in as user, & forgot iMac password.

So a few years ago, I must have deleted a file that kept asking me for passwords on my iMac, I figured I didn't need it since I am the only user. This week I did an OS update, and it asked my my computer password, not my Apple ID. I typed it in, and it did not work. I did the "command" R startup to utilities, and then terminal to reset the password, but on the square box where the list of users would be, there are no names, it is totally blank. I can't seem to find any other way to do this. I reinstalled Catalina OS and it did it fine, but still the same problem. My iMac is from late 2012, and it runs from an external SSD. Any suggestions? Thanks.