View the original community article here
Last tested: Sep 21, 2020
No, you may not custom sort the explores. They will be sorted alphabetically.
The workaround is to use spaces or underscores to change the alphabetic ordering since those characters aren't rendered in the explore menu. It also sorts uppercase and then lowercase, so you can use label in the explore’s LookML to give it the same name with a lower case to bring it to the end