Which limit are you looking to increase?

export default {
  fetch: app.fetch,
  async queue(...) { ... }
}

export default {
  fetch: app.fetch,
  async queue(...) { ... }
}

// Any contentType other than "v8" cannot be handled in the DLQ
env.MY_QUEUE.send({ foo: "bar" }, { contentType: "json" });

// This is handled fine by the DLQ consumer worker
env.MY_QUEUE.send({ foo: "bar" });
// This is also fine
env.MY_QUEUE.send({ foo: "bar" }, { contentType: "v8" });

// Any contentType other than "v8" cannot be handled in the DLQ
env.MY_QUEUE.send({ foo: "bar" }, { contentType: "json" });

// This is handled fine by the DLQ consumer worker
env.MY_QUEUE.send({ foo: "bar" });
// This is also fine
env.MY_QUEUE.send({ foo: "bar" }, { contentType: "v8" });

export interface Env {
    MY_QUEUE: Queue;
}

export default {
    async fetch(req: Request, env: Env): Promise<Response> {
        // Any contentType other than "v8" cannot be handled in the DLQ
        await env.MY_QUEUE.send({ foo: 'bar' }, { contentType: 'json' });
        return new Response('Sent message to the queue');
    },

    async queue(batch: MessageBatch<Error>, env: Env): Promise<void> {
        // Due to this error, the event will end up in the dead letter queue
        throw new Error('Foobar');
    },
};

export interface Env {
    MY_QUEUE: Queue;
}

export default {
    async fetch(req: Request, env: Env): Promise<Response> {
        // Any contentType other than "v8" cannot be handled in the DLQ
        await env.MY_QUEUE.send({ foo: 'bar' }, { contentType: 'json' });
        return new Response('Sent message to the queue');
    },

    async queue(batch: MessageBatch<Error>, env: Env): Promise<void> {
        // Due to this error, the event will end up in the dead letter queue
        throw new Error('Foobar');
    },
};

export default {
    async queue(batch: MessageBatch<Error>, env: Env): Promise<void> {
        console.log(`Events received: ${JSON.stringify(batch.messages)}`);
    },
};

export default {
    async queue(batch: MessageBatch<Error>, env: Env): Promise<void> {
        console.log(`Events received: ${JSON.stringify(batch.messages)}`);
    },
};