Hello,
I know the requirements but I have a client whose host will not upgrade MySQL so I want to ask before attempting to update WP.
Speaking of requirements, PHP 7.4 has been end of life for nearly a year yet you state that as the minimum version. It should be PHP 8.x.
The minimum version for MySQL was bumped three years ago: https://make.ww.wp.xz.cn/hosting/handbook/compatibility/
So it’s not officially supported. Maybe talk again with the host or switch hosts?
It does look like WP will still upgrade even if the version is 5.6: https://github.com/WordPress/wordpress-develop/blob/5fab14051188f87335ed5efdf5e199cf8517149f/src/wp-includes/version.php#L47
But I wouldn’t recommend that at all, I have no idea if there’s anything that could break.