SJD06

So this has been happening to me recently too, and from what I can tell, Quark is the problem. I had forgotten to add it into a personal modpack and put it in (1.16.3), and all the sudden loading my world gave me the error. I thus removed it and carried on, but when adding some other cool mods I found, it happened again and removing the new mods doesn't work anymore. This is on the new curseforge launcher if that changes anything. Just ask if you need any info, I'd be glad to help.