by Ken Task.
Go to Server -> PHP info.
Top 3 lines of that might give more info than x86_64-redhat-linux-gnu.
If you see el7 in there that's CentOS 7.
I have a 3.11.highest and just tested backing up a course ... no issues.
PHP is 7.4.33. Also have a 4.0.8+ on same server.
That version of Moodle is using course backups in background ... as default ... but I usually don't go on to other things and wait until I see backup complete.
No issues with it either.
The other factor .... plugins/addons. Full debugging on and attempting a backup might show more info ... and point to a specific addon that's the issue.
'SoS', Ken