you can find out which zone is mapped to use1-az4 for your account with awscli: ...

mnordhoff · on Dec 22, 2021

Or if you open the EC2 console (it's up this time!) and scroll down to the bottom.

https://console.aws.amazon.com/ec2/v2/home?region=us-east-1#...:

(Edit: I hope I didn't sound sarcastic. I don't open random console pages and scroll all the way down to check for new features. Some people will have noticed, some won't.)