did not see ipv4 ip address charge in N. Virginia Region EC2 Instances

Hello.

I think that even if you are using the Northern Virginia region, the charge for public IPv4 addresses will be listed in the VPC item.
Did you use public IPv4 addresses in the Northern Virginia region?
It's also possible that it just takes a while for it to appear on your bill.
https://aws.amazon.com/vpc/pricing/?nc1=h_ls

In what AWS locations does public IPv4 address pricing apply?
In-use and idle public IPv4 address pricing applies across all AWS commercial, US GovCloud, and AWS China regions, and AWS Local Zones.

If you believe this is a billing error, we recommend that you open a case with AWS Support under "Account and billing".
Inquiries under "Account and billing" can be made free of charge.
https://docs.aws.amazon.com/awssupport/latest/user/case-management.html

i contacted them and the support aren't able to answer the question and i don't know if its ok to let it go.

also to answer your question, i did attached the IPv4 via aws ec2 launch auto assign ip address. but the only thing i did not do is to access the server via ip address, i just had to do some tests so i launched the ec2 for 1 hour and then deleted it.