As a legacy version, 5.6.3 has developed several significant maintenance challenges for those still running it:
Compatible with Macs capable of running High Sierra, including Late 2009 MacBooks and iMacs, and Mid 2010 Mac minis, Pros, and MacBook Pros. macOS Server 5.6.3
Does 5.6.3 delete deprecated services? - Apple Support Community As a legacy version, 5
and integrated directly into the standard macOS System Preferences. Critical Post-Release Issues (2020–2025) As a legacy version
(Mail, DNS, DHCP, VPN, Websites, Wiki, Calendar, Contacts)