Will I lose my Gold Points if I change the country of my Nintendo Account?
Gold Points can only be used in a country that uses the same currency as the country where you earned them.
The points you haven't used yet remain in your account until they expire, but will only be displayed on My Nintendo if they can be used with your current country setting.
If your account is set to Germany and you have earned 250 Gold Points, you can change the country for your account to France and still use these 250 Gold Points for a purchase on Nintendo Switch, since both countries use the Euro as their currency.
However, if you change your country to the UK, you will no longer be able to use these 250 Gold Points, since the currency in the UK is different from France and Germany.
Changing your country/region settings back to Germany would allow you to use the 250 Gold Points again.