This article was originally published on my personal website: Deleting Cloudflare Pages projects with many deployments

Small number of deployments

If your deployment count is only one or two hundred, you can try manually deleting old deployments. Delete until the deployment count is less than one hundred, and then you should be able to delete the project.

Large number of deployments

You need to use Cloudflare’s API to delete deployments, and you need to install Cloudflare CLI to perform this operation.
This part has been covered by others in tutorials, so I won’t repeat it here. You can refer to this article.