Suggestion: Create an option to use JSON values instead of unknown.

Instead generating unknown types, e.g.:

[k: string]: unknown;

I would suggest:

type JsonObject = {[Key in string]: JsonValue};
type JsonArray = JsonValue[] | readonly JsonValue[];
type JsonPrimitive = string | number | boolean | null;
type JsonValue = JsonPrimitive | JsonObject | JsonArray;
type JsonProperty = JsonValue | unknown;

...

[k: string]: JsonProperty;

I'd actually suggest this be the default behavior, with an option to disable it, and a version bump, but that might be too extreme.