Typescript errors while destructuring foreach from object.entries output

I am having certain types that are categorized based on mimetypes

export type MimeType = 'image' | 'application' | 'text';

export type ApplicationMimeType = '.pdf' | '.zip';

export type ImageMimeType = '.gif' | '.png' | '.jpeg' | '.jpg' | '.svg' ;

export type TextType = '.csv' | '.txt';

export type ExtensionTypes = ImageMimeType[] | ApplicationMimeType[] | TextType[];

export type FileType = {
  image?: ImageMimeType[];
  application? : ApplicationMimeType[];
  text? : TextType[]
};

Now when I use it in a function, then use Object.entries when a certain object is passed, the key type is set to string. Is there a way for this key to be set to the type of MimeType?

I tried the solution that is given in this link: Typescript Key-Value relation preserving Object.entries type

Code I tried that is giving me error Type 'undefined' is not assignable to type 'string[]'.

How can I restrict key to be MimeType and extensions to be ExtensionTypes

export type Entries<T> = {
  [K in keyof T]: [extensions: T[K]][];
}[keyof T][];

export const getAcceptedFileTypes = (mimeTypes: FileType) => {
  const acceptedTypes = {};
  Object.entries(mimeTypes as Entries<mimeTypes>).forEach(([key, extensions]) => {
    if (key === 'text') {
      acceptedTypes['text/*'] = extensions;
    } else if (key === 'image') {
      extensions.forEach(
        (image) => (acceptedTypes[`image/${image.substring(1)}`] = [image])
      );
    } else {
      extensions.forEach(
        (application) =>
          (acceptedTypes[`application/${application.substring(1)}`] = [
            application,
          ])
      );
    }
  });
  return acceptedTypes;
};

getAcceptedFileTypes({ image: ['.png'], application: [] })