https://americansabroad.org/issues/taxation/us-tax-implications-of-a-non-american-spouse/
Married filing jointly is a bit complicated, but the above article gives you a good idea
Regards Jane Bruno's article which lyonaria has provided, and in particular the following extraxt from
"1. Choose to treat spouse as resident alien for tax purposes.....
But in later years you can file joint or separate returns."
The statement is precise and correct, and is found in Publication 54. When this option is elected, unfortunately, many interpret its meaning incorrectly. The US spouse may file either jointly or separately in any year other than the first, but naturally, they must file
every year since they are a US citizen. The (UK) spouse, if the option is elected, may also file jointly with the US spouse, or separately, BUT, what most miss is the requirement that the UK spouse must also file
every year, even if filing separately from the US spouse. They become liable to the same filing requirements as a US citizen, the requirement to file a US tax return every year they exceed the filing threshold.