Maine gives back all of paid tax to military members. Why is that tax break not getting applied to me?

You are correct.  If you are active duty military, and you are stationed in a state other than Maine, Maine does not consider your income to be taxable there.  To exclude this income in TurboTax:

1. Ensure that you have marked yourself as Active Duty Military in the Personal Information section
2. Ensure that you mark that your W-2 is active duty military pay in the screen just after entering your W-2 into the system.
3. In the Maine resident return, keep scrolling through the screens until you get to the screen marked Non-Maine Active Duty Military Pay Subtraction.  In the box on that page, enter in the amount of your military pay that you earned stationed outside of Maine (if you were stationed outside of Maine all year, this would be all of your income).

The following screenshot from the Maine return should assist you:

Under which section is this screen? I know it's in the state return section, but it doesn't show up when I click through all the state return screens.

Where in the State interview for Maine for 2018 does "Non-Maine Active Duty Military Pay Subtraction." pop-up?

@Anonymous  You will not get that "pop up" unless you follow the first two steps (in the federal section of the program)

1. Ensure that you have marked yourself as Active Duty Military in the Personal Information section
2. Ensure that you mark that your W-2 is active duty military pay in the screen just after entering your W-2 into the system.

Then in the ME section, you will be asked to confirm your military status.  That will automatically generate the "Non-Maine Active Duty Military Pay Subtraction."

That has been checked already.   Personal info already has Residency of Main, and subsequent Active duty Q&A are filled out, along with the W-2 indicated a Active Duty.  I Removed the State return and started it over as well, and still no screen for this generates.  Where in the State interview is this supposed to appear?

@Anonymous 

Just checking...you are working on a 2018 or earlier year  tax return aren't you?

_________________________________

IF you are starting on 2019 taxes, I doubt the state parts will work properly until sometime in mid-Jan-to-mid-Feb.  Some years they let you download the state software long before they have all the links and calcs ready yet...one year TTX let me download the NC forms, but the state forms were all from the year before NC did a complete layout change......so everything messed up until the actual January state forms release.

For Military Personnel whose Home Of Record is Maine and are you are stationed in another state, to get this question to generate:

In the State return, Update your Residency in the General Info section,

Then "Change Residency"

Then Choose "Safe Harbor Resident."

State of Domicile & state of legal residence, would be Maine.

After updating State Residency, visit the Adjustments section.

After several click under Adjustments, a page will populate titled "Nonresident Military Compensation Subtraction."

Enter in your Military wages here.

Additional follow-up pages will ask about your Military wages.  Enter only your Active Duty Military Wages as a subtraction.

Your State refund/Amount due will adjust after updating these entries.

This was great in 2019 can we get an update for 2021 tax year. thank you

The steps for 2021 are exactly the same as outlined by @kczigmant.   First be sure you have indicated in the federal "My Info" section that you are active duty military.  Next verify in the "Income" tab that in the follow on question after entering the military form W2 the "Active Duty Military Pay" option was selected.  

You can then continue the Maine state interview.

1. "Change Residency"
2. "Safe Harbor Residency"
3. You didn't move into or out of Maine and you were not a non-resident ("No" to all three questions)
4. State of Domicile is "Maine"
5. Enter two-letter state code for the state where you were stationed on 31 Dec.
6. Enter "Maine" as your state of legal residence
7. Continue answering questions and eventually you will arrive at the "Nonresident Military Compensation Subtraction" page which should be populated already