Seeking Advice on Defining types correctly

export const ApiKeyMetadataBrand = Symbol.for("ApiKeyMetadata")
export const ApiKeyMetadata = S.struct({
  name: ApiKeyName,
  createdAt: S.dateFromString(S.string),
  createdBy: GithubLogin,
  lastUsedAt: S.optional(S.dateFromString(S.string)).toOption(),
  identifier: NonEmptyString,
}).pipe(S.brand(ApiKeyMetadataBrand))
export type ApiKeyMetadata = S.To<typeof ApiKeyMetadata>

// this code doesn't have much importance for my issue. It's just to give you the context
const map: HashMap<Project, Chunk<ApiKeyMetadata>> = ...
const newMap = HasMap.modify(projectA, Chunk.append(metadata))(map)