The article says, "You can't rename the same account from where you're performing the rename. Use the command line maintenance script to do the rename, or use a different account to do the rename."
I'm in the
maintenance folder, but there does not appear to be a script to perform the rename:
# ls |grep -i rename renameDbPrefix.php renameRestrictions.php
I'm using Mediawiki 1.35.2, if it matters.