I'm also interested in getting this question answered (for tax year 2024). In my case, I want to know how to report a 1099-B for a joint account with my sibling (our grandparents gave us a joint asset as a gift). Clearly, I'm not going to file taxes jointly with my sibling. But that leaves us with two reporting options, right?
a.) Both of us report exactly what is on our 1099B form (verbatim), which means we're double counting proceeds/withholdings.
or
b.) Both of us report the proceeds/withholdings as if they were divided in half, which won't match the 1099B form we received.
Which is best?
