I have also the same problem
After upgrading from moodle 3.5.3 to moodle 3.6.1 I have my moodle site inaccessible with blank page and same message
I had to remove the whole website and started from scratch
I have also the same problem
After upgrading from moodle 3.5.3 to moodle 3.6.1 I have my moodle site inaccessible with blank page and same message
I had to remove the whole website and started from scratch