The way I read the IRS instructions, in my husband's case as a K1 in AoS limbo who doesn't meet the residency tests (green card/substantial presence test), if we choose to file Married Jointly then we must submit a letter stating that we are electing to have him treated as a resident alien. At that point we follow the rules of reporting for a resident alien.
"Generally, a married couple can't file a joint return if either spouse is a nonresident alien at any time during the year. However, if you were a nonresident alien or dual-status alien and were married to a U.S citizen or a resident alien at the end of 2021, you can elect to be treated as a resident alien and file a joint return. See Pub. 519 for details."
Pub 519 pg 9 "Nonresident Spouse Treated as a Resident"
"If, at the end of your tax year, you are married and one spouse is a U.S. citizen or a resident alien and the other spouse is a nonresident alien, you can choose to treat the nonresident spouse as a U.S. resident. This includes situations in which one spouse is a nonresident alien at the beginning of the tax year, but a resident alien at the end of the year, and the other spouse is a nonresident alien at the end of the year.
If you make this choice, you and your spouse are treated for income tax purposes as residents for your entire tax year. Neither you nor your spouse can claim under any tax treaty not to be a U.S. resident. You are both taxed on worldwide income. You must file a joint income tax return for the year you make the choice, but you and your spouse can file joint or separate returns in later years."
So if I'm reading this right, my husband would be treated as a resident alien and either the second or the third bullet would apply? It does not specify that it has to be 2021 tax year just a tax year/any period of 12 consecutive months.
This is where my confidence drops. At the same time, my husband didn't make more than $30k last year in France so it shouldn't be that bad for us per what Wuozopo stated.