I can't find ModSecurity or Fail2Ban management tool in Plesk GUI, why?
Security Core (ModSecurity and Fail2Ban) may absent because license key has no corresponding property or it was just not installed on server.
To check whether the license key supports it, go to:
Server Management > Tools & Settings > License Management
and see if there is the line "Security core (ModSecurity and Fail2Ban)".
You can install Fail2Ban component under
Tools & Settings > Updates and Upgrades > Add or Remove Components > Fail2Ban authentication failure monitor
You can install ModSecurity component in:
Tools & Settings > Updates and Upgrades > Add or Remove Components > Web hosting features > ModSecurity Web Application Firewall for Apache