Ok ... since Nevada has no state income tax that is a mute subject.
AND if the divorce was final as of 12/31/2020 then you do NOT file a joint return because you were no longer married as of midnight on 12/31. If you already did then you need to correct that asap.
Now will the 20% federal withholding be enough ? Be enough for whom ? Did the court issue a QDRO for the retirement distribution ? If so did she get the 1099-R form in her name only ? If so that is her problem to deal with not yours.
