Have biab 2019 windows. In melody input under edit mode can't get an F natural in the key of D. I've tried shift and control key. Any ideas. I couldn't find anything in documentation on accidentals.

try the ALT key and the note.

Have you tried right clicking on the note to set the accidental?

In Editable Notation Mode, right click on the note and you’ll see an option.

Just curious, are you saying you only get an F#?

It's definitely working here with both the <Alt> key or right-clicking and editing.

Make sure you are in Editable Notation Mode.

You can also left click on the note with your mouse and move it down to an F natural.

I tried left clicking and dragging. It goes directly from E to F#.

You have to move the mouse in small increments. In notation mode there is a box in the tool bar that tells you what the note you are on clicked on is ("A 7" for example). That changes as you move the mouse.

Hope this helps.

I tend to move in larger increments, i.e. drop or raise the note several pitches, then drag it to what I want. I find it easier, but whatever works.

Did you try right-clicking and editing the note value? You can then specify the exact note you want.

Do you have your key signature set to D?