Yes, it should work that way to not receive notifications if it's enabled, so sounds like a bug.
"Filtering messages from unknown senders turns off iMessage notifications from senders who aren’t in your contacts and sorts the messages into the Unknown Senders tab in the Messages list."
Block, filter, and report messages on iPhone
In Messages on iPhone, block unwanted messages, filter messages from unknown senders, and report junk or spam messages.support.apple.com
It certainly seems like it should silence notifications as well (as it used to before iOS 14 when it didn't apply to regular text/SMS/MMS messaging). Unfortunately it makes the feature that much less useful. Something I've also brought up in a similar thread:Other than routing to different folders, what does it do? I still get alerts for messages sent to the Unknown folder, and from what I’ve read that’s not supposed to happen with this feature enabled. So I’m a bit unclear.
It used to that before iOS 14 when that option was limited to iMessages, but for some reason since iOS 14 when it was expanded to cover regular text/SMS/MMS messaging the notification silencing part of it got dropped. The latest support documentation and wording around the option only refers to it filtering messages and no longer mentions anything about notifications:Yes, it should work that way to not receive notifications if it's enabled, so sounds like a bug.
"Filtering messages from unknown senders turns off iMessage notifications from senders who aren’t in your contacts and sorts the messages into the Unknown Senders tab in the Messages list."
Block, filter, and report messages on iPhone
In Messages on iPhone, block unwanted messages, filter messages from unknown senders, and report junk or spam messages.support.apple.com
It seems like that's what it has turned to as of iOS 14. Prior to that in addition to actually filtering ("cleaning up") things in the Messages app it also silenced notifications for those messages (although only applied to iMessages).I was under the impression that this simply cleans up the Messages app to hide threads from companies etc that are not in your contacts etc?
In that link you provided it actually does mention that turning on the “Filter Unknown Senders” should disable notifications. I don’t have the setting enabled, so I can’t confirm how it behaves on my device, but it seems like a bug if notifications are still coming through for unknown senders....The latest support documentation and wording around the option only refers to it filtering messages and no longer mentions anything about notifications:
Block phone numbers, contacts, and emails on your iPhone or iPad - Apple Support
You can block phone numbers, contacts, and emails on your device. You can also filter iMessages from unknown senders and report iMessages that look like spam or junk.support.apple.com
Seems like it might have been updated since the last time I looked through it more thoroughly.In that link you provided it actually does mention that turning on the “Filter Unknown Senders” should disable notifications. I don’t have the setting enabled, so I can’t confirm how it behaves on my device, but it seems like a bug if notifications are still coming through for unknown senders.