"especially if the truck has MFS written on the side of it"

I see MFJ gets 3 EIP #3 letters. The first Joint letter came in April 2021 and notified them that they had $2,800 coming and to expect that. Two separately-named individual letters came in January 2022 and reiterated that they each got $1,400. No matter how you file, it's clear the IRS knows what you got. There is no divorced spouse going to be able to argue, "He got my money, so I want more."