How to disable Gutenberg editor from Multisite Admin panel?

You can programmatically disable Gutenberg network-wide by adding a must-use plugin containing this code:

<?php
add_filter( 'use_block_editor_for_post', '__return_false' );

References

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)