Box 19 and 20 (for WA residents) is only needed if you itemize deductions on the federal return. If you don't itemize, leave boxes 15-20 blank at the W-2 screen.
There's currently a glitch in TT and we don't know when it's gonna be fixed. WA should be there. If you do itemize and it won't let you proceed without putting something in box 20, put any state in.