I have deleted my administrator account and now can’t log into my computer at all

First please confirm you are still using macOS 10.13 "High Sierra" as shown in the profile information below your post.

• If not, please identify the macOS version you are using: Find out which macOS your Mac is using - Apple Support
• If so, you can use the procedure in the following Discussion: admin has disappeared in Big Sur - Apple Community

That specific procedure was specifically written and tested for Big Sur, but it should be valid for High Sierra.

In case you are interested, this older Discussion described the same procedure for High Sierra. Being older, it lacks the additional details I subsequently added for clarity.

In any case, if something in it does not work as described, please come back here and describe the specific step that is not working.