My brother and I cannot play Minecraft Java Edition together on LAN

I recently purchased a copy of Minecraft Java + Bedrock edition for my older brother this holiday season with the intent of us to be able to play the game together. However, we have had multiple issues whenever we try to play together on the latest version of Java. Whenever I host a world, it appears on his screen of joinable games on the multiplayer screen. However, his worlds do not appear on my screen. He clicks on the new world for us to play on to join it, and then he is greeted with an error message saying that the game has failed to connect to the server. We initially thought it was due to using a Forge client for 1.20.1 with only Opitfine, a mod that adds no new gameplay elements and just allows for the game to render Resource Packs and to perform better. So, we decided to try playing the latest release without mods. The same problem persists, he is unable to join my worlds, and his worlds do not even show on my multiplayer screen. We have tried countless solutions from YouTube videos such as turning off our firewalls and directly connecting to my world with a code, but the same problem persists. Both of our PCs are powerful enough to run the game, and my PC is even capable of playing heavily modded versions of the game like RLCraft and GregTech: New Horizons. Is his account too new to play on multiplayer words, or is it something else that I am missing? His account is only a few weeks old, while mine is over 6 years old. I just find it odd that we struggle to play the normal game with no mods in the same room, but players from around the world have no problem connecting to and to play heavily modded multiplayer servers.

:)