How to remove Elastic IPs from Elastic Beanstalk Environments?

Hello.

Are you running a single instance?
In that case, the CloudFormation template includes the creation of ElasticIP when creating the ElasticBeanstalk environment.
I thought it might not be possible to delete it if you are using a single instance. (You may be able to remove ElasticIP from the EC2 console, but I think it may break your Elastic Beanstalk environment.)
https://docs.aws.amazon.com/elasticbeanstalk/latest/dg/using-features-managing-env-types.html

A single-instance environment contains one Amazon EC2 instance with an Elastic IP address. A single-instance environment doesn't have a load balancer, which can help you reduce costs compared to a load-balanced, scalable environment. Although a single-instance environment does use the Amazon EC2 Auto Scaling service, settings for the minimum number of instances, maximum number of instances, and desired capacity are all set to 1. Consequently, new instances are not started to accommodate increasing load on your application.

Use a single-instance environment if you expect your production application to have low traffic or if you are doing remote development. If you're not sure which environment type to select, you can pick one and, if required, you can switch the environment type later. For more information, see Changing environment type.