When using the messenger app or any app so which you needed to text when pulling out your S Pen pointing in the left corner then a blue T which show up then another window with open allowing you to reply or comment using your S Pen to text.
On my Note 10 plus disability is no longer available.
How does one get this function back?
Is this what you're referring to? You can find the write to text icon on the keyboard.
I've never used this feature on previous Notes, so I'm not familiar with where it was placed previously.