I'm using the Bitbucket integration. For every commit to the main branch, I see a release listed under Releases. This happens automatically without me doing anything.

How do I disable automatic releases from a main branch to only create releases from the release branch?

You could go to your repository settings on BitBucket > Webhooks > sentry-bitbucket-repo-hook (or a similar name related to sentry) > Edit > Triggers.

There, you will see that the webhook is called when a push happens.

You want to disable that, and have it work only when a pull request is merged.