STOP .... you MUST file correctly ... if the divorce was final as of 12/31/20 then you CANNOT file a joint return. As of the stroke of midnight on 1/1/2021 if you were not considered married then you are not married for the 2020 tax return even if the judge signed it one minute before midnight.
Until you are sure on that point then you cannot move forward. If you WERE still married then you need to discuss this with her to decide how you will file ... she must agree to file jointly otherwise your ONLY option will be to file separately. Work the numbers both ways and make a joint decision if you both can agree to do so.
If you are divorced as of midnight then your ONLY choice will be to file single. Same for her and if she got the distribution in her name and choose not to roll it into another retirement plan then that is her problem not yours.
