Upwork does not currently have a special field for displaying "which country I would like to offer services to."
If you want to offer services to clients living in China, you may do so. You may even indicate this in your profile overview text.
With regards to your place of residence, as displayed on your profile page, that is "where you live now."
That is not intended to indicate your nationality or preferred client location.
So Germany is the correct information, and Upwork wants you to leave that as "Germany".
If you move out of Germany to some other place, then Upwork can help you update that information if necessary.