Steps to reproduce:

1. Configuration->Actions->Create Action (Event Source: Triggers)
2. Click Operations->New, choose 'Remote Command' for type
3. Choose 'Zabbix Server' for Execute On field
4. Enter your custom script
5. Click 'Add' for the operation

Result:
UI won't save and gives error message: "You did not specify targets for action operation command"

Expected:
Allowed to save without specifying target host.

Per documentation: "The target list is meaningless if a custom script is executed on Zabbix server. " [Ref|https://www.zabbix.com/documentation/5.0/manual/config/notifications/action/operation?s[]=target&s[]=list]