admin/environment/custom check/php not 64 bits
From MoodleDocs
This message means that your current PHP version is not 64 bits.
A new feature of PHP7 is it has now 64-bit version so it can use more than 4GB RAM and code performance can be potentially two times faster depending on the application design.
Note: Since Moodle 4.2 it's required to use a 64-bit version of PHP and the underlying Operating System.
