- Create media type
- Create action an choose "Recovery operations" or "Update operations" (but do not choose "Operations").
- Select "Send message to" and "Send only to" and then choose that media type.
- Go to media types and observe there is nothing in "Used in actions". Try to delete the media type and system won't allow it.
Related issue and still reproducible: https://support.zabbix.com/browse/ZBXNEXT-4165
This issue is about choosing "Send only to" option "
All" and then similarly the column "Used in actions" is empty.