Search Problem for Network Admin Users Screen

You wish to search users by registration date? Why wouldn’t you simply click on the Registration column head so the table is sorted by date? It should be relatively easy to find the date you are looking for in an ordered list.

If you really need a date search field, you can adapt the selected answer’s code in your link to collect date search criteria instead of selection from a dropdown. Then modify the post query with date_query instead of a meta_query.