This seems to be a Turbotax decision. Odd, but there it is.
"Posted February 22, 2019 I did one of these today. Spouse is a US citizen and husband lives in another country. Return was MFS, and I just marked the box that he was a nonresident alien. No problem with efile." https://www.atxcommunity.com/topic/21416-file-mfs-but-no-ss-number-for-non-citizen-spouse/
"you must print your return and file by mail. Prepare your return in TurboTax. When you get to the Let’s get ready to e-file screen, select File by Mail. TurboTax will give you an error...
https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-credits-deductions/[product key remo...
