See Release Notes
Long Term Support Release

• Bug fixes for general core bugs in 3.9.x will end* 10 May 2021 (12 months).
• Bug fixes for security issues in 3.9.x will end* 8 May 2023 (36 months).
• PHP version: minimum PHP 7.2.0 Note: minimum PHP version has increased since Moodle 3.8. PHP 7.3.x and 7.4.x are supported too.

• Moodle 3.9 Database Schema (by Marcus Green)