I finished updated "Certificate authority" For Amazon RDS but still receiving mail "Update Your Amazon RDS and Amazon Aurora SSL/TLS Certificates by August 22, 2024"

Hello.

Does the "Databases requiring certificate update page" show which clusters or RDS instances need updating?
I think it would be a good idea to check other regions just to be sure.
If the RDS instance etc. are not displayed on this page, I think it is safe to ignore the email.
https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/UsingWithRDS.SSL-certificate-rotation.html#UsingWithRDS.SSL-certificate-rotation-maintenance-update

I see one instance on AWS RDS, but when I check that instance then it has been updated. Please check below image. And I still received email last night. So what should I do with this email?

Is there an instance listed under "Certificate update"?
Looking at the image you shared, it doesn't appear to be listed under "Certificate update".
If the instance is not listed on the "Certificate update" page, there is no need to take any action.
I think the email is probably sent periodically in batches or something, so I think it was safe to ignore it as long as it had already been dealt with.