The game crashes on startup.
Everything else is in the crash log.

Quick question did you download the mod from Modrinth? and if so does the jar end with -dev.jar? It does look like you may be trying to load the -dev.jar

Yes, that was the problem. I have now downloaded the mod from curse forge, and it works fine.

@FlashyReese Would you be able to remove the -dev version from Modrinth featured versions and add the real 1.2.1?
Since this will confuse more people.

I was just about to file another issue when I found this. 😄
Thanks

EDIT: I just found out that you have the normal version present on Modrinth. However when clicking download on the main version page, Modrinth automatically serves the -dev.jar.
Is this a bug with Modrinth or can you configure it differently?