If it helps, Forge is confusing about which version they support. In the official minecraft loader, forge also crashes for version 1.20.3. Here is the crash:
crash-2023-12-17_18.47.10-client.txt

On https://forums.minecraftforge.net/topic/125488-rules-and-frequently-asked-questions-faq/ webpage, they say, 1.20.3 is not supported, but 1.20.4. On https://forums.minecraftforge.net/topic/91712-supported-version-directory/ page, they say, they neither support 1.20.3 nor 1.20.4. On the official download page, there is no stable version for these two minecraft versions. If anyone found the solution, I'm interested in the solution, as I'd like to know, which versions are ready to be modded.

the forge forums are pretty much abandoned as the project split into neoforge

either way with my patch here you can get to the launch state phit/multimc-meta-scripts@24642e8 but there's probably some more work left to do in forgewrapper / or ideally just rip out forge and replace it with neoforge for newer mc versions

Thanks for clarifying that! I thing I'm going to switch to NeoForge then.

Hey, I'm not sure if this helps with Linux, but I'm on Windows, and noticed an issue with this. The web URL that is called does not match what it should be.

What is called is:
https://maven.minecraftforge.net/net/minecraftforge/forge/1.20.4-49.0.19/forge-1.20.4-49.0.19-launcher.jar

When going to that site, it says you want files.minecraftforge...like this:
https://files.minecraftforge.net/net/minecraftforge/forge/index_1.20.4.html (this isn't where that jar is actually located, because there's a download installer button on this page).

yes none of those URL's are correct, please see the linked issues, the proper fixes are ready and are just waiting to be merged

Hello, still in progress ? I tried to see in forge installer if there is any of those url but don't work and manual install from the instances folder "1.20.4/.minecraft" using "java -jar forge-1.20.4-49.0.22-installer.jar" doesn't do anything.

waiting on MultiMC/meta#17 to be merged

Pretty nice !
Works well now, thanks you so much, actually it's seems work fine with Forge 49.0.22
I love to see it in the new update