Which HTTP status Code means that the server cannot or will not process the request because of perceived client error?

The 100 Continue code is an informational (1xx) response indicating the server received the request headers and the client should proceed to send the request body.

The 203 Non-Authoritative Information code is a success (2xx) response indicating the returned metadata was retrieved from a third-party copy rather than the origin server.

The 303 See Other code is a redirection (3xx) response directing the client to retrieve the resource at a different URI using a GET request.

The 400 Bad Request status code is defined in RFC 9110 as the server's response when it cannot or will not process the request because of something perceived to be a client error - such as malformed request syntax, invalid request message framing, or deceptive request routing. It is the generic client-side error at the beginning of the 4xx range.