Hello, I am currently fighting against the error #3495 but in 1.19.4, I would like to know if it is possible to fix it in some way please

Are you a mod developer or just a player? If you are a developer, what are your usage that makes it need to be a local handler instead of global one?

I am trying to send a packet to the player when entering the server, according to what I searched in the discord channels of the same fabric, a person had the same error, and changing that solved it but in 1.20.X, I would like to know if changing that Well, it would be fixed, or is it something that I keep doing wrong?

Have you actually registered the response handler?
Alongside the client-side request handler, you also need to register the server-side response handler.
The client request handler returns a future packet that needs to be handled on the server.