After installing Json, it crash the game in the loading scren.
There is not crashlog, just the latest log.

NeoForge 21.0.56
JsonThings-1.21-0.12.0.jar
rhino-2100.2.5-build.41.jar

Logs

latest.log

Hmm, that log doesn't say anything that all that would point to JsonThings.
Is there a debug.log? If you are using CurseForge as it seems like from the paths, you will need to enable it in the settings.
If a debug.log doesn't show any errors, you may need to enable the "show output window" option in the vanilla launcher curseforge opens when you launch a pack.

Hi, attached you will find the debug log

debug.log

Thanks! I have looked at it but I don't see anything that indicates what the error may be can you join the Neoforge discord server and show this debug log on the user-support channel there?

I just posted on the user support channel