Downloading files bigger than 10 MB ($filesize > 10000000) from assignments, files, folders etc. fails. I found this Apache error with debugging (DEVELOPER) on: mod_fcgid: stderr: PHP Warning: Cannot modify header information - headers already sent by (output started at /path/to/moodle/lib/filelib.php:2239) in /path/to/moodle/lib/filelib.php on line 2247, referer: https://example.com/mod/folder/view.php?id=20

If I add two zeros to filelib.php:2239 ($filesize > 1000000000) then it works because the code from line 2239 until 2243 is not executed. I tested downloading files up to 230 MB which failed without the two zeros. I'm on an environment with Plesk and use PHP 7.2 run as FastCGI application served by Apache. I discovered the issue while upgrading (Git) from Moodle 3.6. I tried to replicate it with the Moodle Sandbox but there it works just fine.