It does allow it for SMS apparently, but the UI is easy to misunderstand. In the "Unknown & Spam" settings where you picked "Filter Unknown Senders" there is an option below it marked "SMS Filtering" and you need to set that to... "SMS Filter".
Even if it couldn't do this, that would just bolster the case that Apple is making SMS worse than it has to be on their platform to promote iMessage and its network effects.
EDIT: I booted up my iPhone 14 on the latest iOS and I guess this has changed? There isn't a "SMS Filtering" option near the Filter Unknown Senders option which has moved to the top level Messages settings page versus when the guide was written.
I'm not sure if that means it always filters SMS or it never does, but again if it doesn't filter SMS at all that's an Apple choice, it doesn't mean you can't do it on SMS.
https://www.guidingtech.com/how-to-block-text-messages-from-...
Even if it couldn't do this, that would just bolster the case that Apple is making SMS worse than it has to be on their platform to promote iMessage and its network effects.
EDIT: I booted up my iPhone 14 on the latest iOS and I guess this has changed? There isn't a "SMS Filtering" option near the Filter Unknown Senders option which has moved to the top level Messages settings page versus when the guide was written.
I'm not sure if that means it always filters SMS or it never does, but again if it doesn't filter SMS at all that's an Apple choice, it doesn't mean you can't do it on SMS.