Related to the closed MC-231561 when a player join to a server if the server its outdated show a message like the cliente its outdated and not the server also the messages for multiplayer.disconnect.outdated_client and
multiplayer.disconnect.outdated_server are the same then in any case the message show is client outdated.
Replication:
Run a server in 1.19.3 (can be any only need make sure the server is old than the client)
Try to join using 1.20.4
When join the server show outdated client and show to use the server version
Notes:
In NMS the check where decide what message use looks hardcoded to 1.16.x
The messages are correct, the client is incompatible with the server. It's not saying "outdated client", that would be wrong. Incompatible is perfectly fine.
This is a change request, not a bug.
Your summary and description also do not appear to be saying the same thing.