Which AWS service, tool, or feature will meet this requirement?

Explanations:

AWS PrivateLink is used to securely access services over a private network, not for stateless network filtering.

Security groups provide stateful filtering, which tracks connection states and is not purely stateless.

Network ACLs are stateless and filter traffic at the subnet level, meeting the requirement for stateless filtering.

AWS WAF is a web application firewall that filters HTTP/S traffic, not general network-level filtering.