I upgraded to Moodle 3.9 at the same time I create a new VPS running CentOS 8 (I know, not the smartest thing to do changing two things at the same time.) My old system was running Moodle 3.8 on CentOS 7. I was surprised to see the different requirements for file permissions. Don't know if anyone ran into this or not:
3.8 on CentOS 7
-- moodledata apache:apache 755
-- moodle root:root 755
3.9 on CentOS8
-- moodledata apache:apache 777
-- moodle root:root 755
Moodledata would not run without 777. I had to change /moodle/mod and /moodle/themes to 777 to install a theme and some plugins.
Don't like the idea of 777 file permissions; but I am up and running.