there's a #notedeck UI bug right now for very long composed notes that hinders you from seeing the 'post now' button. the button gets pushed down below the bottom of your screen.

the temporary fix:

option 1) use the keyboard shortcut to post with control + enter.

option 2) zoom out! press control + - to zoom out and then control + +/= to zoom in.

the team is aware and will work on a fix.