Amplify can't depoy second app. Max number of apps reached.

The issue you're experiencing is likely related to webhook limitations imposed by your Git provider rather than AWS Amplify quotas. AWS Amplify Hosting previously created a new webhook for each app associated with a repository, which could quickly exhaust the webhook limits set by Git providers like GitHub, GitLab, or BitBucket.

To address this limitation, AWS Amplify Hosting has recently introduced a new feature called unified webhooks. This feature consolidates all Amplify-related webhooks into a single, comprehensive webhook for a repository. This allows developers to connect multiple Amplify apps to a single repository without being constrained by webhook restrictions.

To resolve your issue and deploy your second Next.js app, you may need to:

1. Reconnect your repository to your Amplify app to take advantage of the new unified webhook feature.
2. If you've reached the maximum number of webhooks allowed by your Git provider, you might need to remove some existing webhooks to make room for the new unified webhook.

Keep in mind that all operations are region-based, so ensure you're working within the same region for all your Amplify apps.

If you continue to face issues after trying these steps, it may be helpful to reach out to AWS Support for further assistance, as they can provide more specific guidance based on your account and setup.
Sources
Simplifying Multi-App Management in AWS Amplify Hosting | Front-End Web & Mobile