You file Joint, as your status is determined as of 12/31/2021.
If you're legally married as of December 31 of the tax year, the IRS considers you to be married for the full year and you can file a joint return.
If you are married you can either file a Joint return or as Married filing Separate. Joint is usually the best way to file. Last year for 2020 you probably each filed as Single (not separate).
A Joint return is one return combined for the both of you. Here's some general info on getting married. Did you both use Turbo Tax last year?
You can not transfer from or combine 2 returns or accounts. Just pick the return for the spouse that has the most complicated return to enter or has any depreciation or business or more investments. Or use the account for whoever you want to be listed first going forward (by the way you can not change the order of the names). Then add the other spouse's name, ssn and info to it.
You should usually file a Joint return which is only 1 return combined for the both of you. Make sure to stick with this one account for the future. Just ignore the other spouse's account.
Getting Married FAQ
And info on Getting Married…..
http://turbotax.intuit.com/tax-tools/tax-tips/Family/Getting-Married/INF12006.html
Is it better to file Joint or Separately?