I'm a "survivor" from that thread. Basically, if you use the simplified AMT Foreign Tax Credit, TurboTax cannot efile your taxes. The IRS made a field required this year, and TurboTax needs to update their software to handle it, but they have decided not to (and their support is mostly really terrible, rude, incompetent, and liars - they definitely won't be able to help you with this issue).
Before a recent update, TurboTax used to allow you to actually e-file with simplified AMT Foreign Tax Credit, but it'd get quickly rejected by the IRS because of that required field. After weeks of waiting and a 15+ page thread, their "solution" was to update the software to block you from e-filing. Seems pretty clear to me that they're not going to fix it.
According to the IRS, it sounds like they'll change it back next year; so hopefully it'll work again for 2021 taxes. Perhaps that's also why TurboTax decided not to bother fixing it 🙄.
I filed by mail earlier this week and asked TurboTax for a refund of my state e-filing fee, though it's been almost a week without a response...
