421 Misdirected Request

The request reached a server that cannot answer for this host, often over an HTTP/2 connection reused for another host.

Class
4xx Client Error. The request has a fault, or cannot be met as sent.
Registered
Yes, in the IANA HTTP status code registry.
Cacheable by default
No. A cache stores it only when Cache-Control or Expires says to.
References
RFC 9110 ยง15.5.20 · MDN

Every 4xx code

All HTTP status codes, in one table