💬 | Drupal core | update.php fails with Multibyte string input conversion in PHP is active and must be disabled.
🇦🇺Australia bushrang3r
OP's php.ini lines did the job for me.
The server was set to "Off" and I was getting the same error until I added the php.ini lines with "0" instead of "Off". No more errors.
mbstring.http_input = pass
mbstring.http_output = pass
mbstring.encoding_translation = 0