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When Focus is enabled for Messages, the notifications, text tones are silenced. However, the messages are still able to be sent.
"When you set a Focus, the icon appears in the status bar and on your Lock Screen, and your status is automatically displayed in the Messages app. When people try to send you a message, they'll see that you’ve silenced notifications, but they can still notify you if it's urgent."
From the article viewed before posting, Use Focus on your iPhone, iPad, or iPod touch
This is in the section titled "Turn on Focus".
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