Last time I checked (a month or so ago), the Form 1040-X in ProSeries was the wrong version for filing certain prior year amended returns.  It appears that the IRS had a form revision in July(?) 2021, that wasn't actually released until around November(?) 2021, and the tax software companies (ProSeries anyway) had not yet had time to get the revised form 1040-X into their software system.  See instructions for form 1040-X on the revision dates to use for the different tax years....then look at the PS version your trying to file (i.e., print preview).