How can we compare married filing jointly with married filing separately in TurboTax Online?
Start by creating a test return so you don't have to undo everything if you decide not to make the change.
Create a test account with its own User ID (include the word "test" in the ID so you can distinguish it from your real account).
Prepare your return(s) using the other filing status. Make sure you also do your state return; you might get a bigger refund on your state return which can offset the additional taxes on your federal, or vice-versa.