Unknownreported this bug
The PreventJockeyMounts option does not prevent Jockey Mounts.
Tested with this mob:
Test:
Type: ZOMBIE
Display: '&aTest Zombie'
Health: 40
Damage: 1
Options:
MovementSpeed: 0.1
PreventJockeyMounts: true
Tested on a clean server with only MythicMobs installed.
Purpur 1.19.3-1913, MythicMobs 5.2.3