by Ken Task.
https://docs.moodle.org/404/en/Environment_-_max_input_vars
There are a lot of big or potentially big forms in Moodle, such as:
Large quizzes and quiz settings
and eventually, before upgrading, one will upgrade MySQL to 8:
If you are using PHP 8 the minimum value of 5000 is required. By default PHP 8 sets to display startup errors (see [1]). This means that the warning about exceeding max_input_vars appears before the workaround even applied.
'SoS', Ken