I guess I misunderstood the issue then.Which still doesn't supress the message about OS Updates, doesn't hide the update button from DA.
By the way, your method doesn't show which packages (OS Updates) are available... so that trick doesn't really help either if it's about updating packages which are under OS Updates (repositories (Yum/Apt etc)).
I thought the issue was, admins were getting daily emails telling them what software had updates and this person was wanting to exclude OS update packages (yum/apt/etc) from being in that list.
My suggestion was to "script it yourself" utilizing the tools provided by DirectAdmin. Yes, you still have to parse the JSON output prior to scripting it to send you an email. But the point was you can give yourself more control of what you're actually notified of. I suppose I didn't address that you'd have to disable whatever system control is sending the original email.
While I'm not opposed to DirectAdmin (and other control panels) sending notifications like the original message, you really can't expect them to have an answer for every single conceivable customization of that message. "I don't want to receive messages about Apache needing an update", "I don't want to receive a message about every PHP version needing an update", "I don't care about phpMyAdmin having an update". At some point, if you don't want to receive messages about some of those item, then you have to take the bull by the horns and script your own solution. Otherwise the DirectAdmin developers are going to be spending all of their time resolving every single minor detail that gets brought up.