I have defined the following types

export interface LanguageEditInfoDto {
    canEdit: boolean;
    label: string;
    useDudenLang: boolean;
}
export type UILanguageEditInfoDto = LanguageEditInfoDto & {
    isFormValid: boolean;
};

and I have defined the following function:

function setLanguages(languages: Record<string, LanguageEditInfoDto>) {
    const langState: Record<string, UILanguageEditInfoDto> = {};
    for (const langCode in languages) {
        langState[langCode] = {
                        isFormValid: true,
                        ...languages[langCode],
                    };
                }

Why do I get the following error for langState[langCode]? AND how to resolve it?

TS2322: Type
{   canEdit?: boolean | undefined;   label?: string | undefined;   useDudenLang?: boolean | undefined;   isFormValid: true; }
is not assignable to type UILanguageEditInfoDto
Type
{   canEdit?: boolean | undefined;   label?: string | undefined;   useDudenLang?: boolean | undefined;   isFormValid: true; }
is not assignable to type LanguageEditInfoDto                   

According to the definition none of the attributes are optional. Therefore the assertion is IMHO wrong.