Thanks, especially for the warning about community property adjustments!
I knew those adjustments applied for state returns (which is part of our reason for doing state as MFJ). But I didn't realize we needed to do that for federal MFS returns.
We ended up filing all 3 returns by paper / mail, due to this warning on the "Tax Withholding Adjustments" screen:
"Note: If you make any federal tax withholding adjustments you will not be able to e-file your federal return, according to IRS rules. You will need to print and mail a paper copy of your federal return".
Seems this would affect any MFS return where either spouse has W2 wages and withholding.
IRS pub 555 (mentioned in the article you linked) includes this:
"If you and your spouse file separate returns on which each of you reports half the community wages, each of you is entitled to credit for half the
income tax withheld on those wages."
