@5nipper , so you a US person ( citizen / Green Card ) are saying that your employer in the USA issued you a W-2 last tax year, showing excess payment and has since corrected the error by reducing monthly payments ? Therefore you are asking for a W-2C because your employer in US gov but the work was done in Germany -- yes ?
Or are you saying that all you are trying get back is the excess taxes you may have paid on the extra 10 K of income or a portion thereof?
I cannot judge the case because surely since they paid and then started reducing your monthly pay packet from the time they were informed, it probably has averaged out as for the taxes ( Fed, FICA etc. ) and W-2 should have been correct. Can you give some dates --- for 2021, when did you receive the bonus, when did they start collecting back and what rate; did the total received for 2021 ( including reduced monthlies ) match the W-2 ?
Please help -- I will circle back once I hear from you . But in general , yes you should get a corrected W-2
