For AWS accounts that are NOT part of the Cornell Enterprise Org, when closing, one faces the same issues as terminating resources then closing. However, without a 3rd party tool like CloudCheckr I can be a rather manual process.
Below are some docs that can assist with walking thru the process.
https://aws.amazon.com/premiumsupport/knowledge-center/check-for-active-resources/
https://aws.amazon.com/premiumsupport/knowledge-center/terminate-resources-account-closure/