If you put datapack with such structure:
datapack_name\data\forge\tags\items\plates\gold.json
It will be impossible to load a world.
But if you override forge with something else, your custom_namespace, everything will be ok.

Here is .json format:
gold.json

Hello, could you share a log file for a world that could not load?

Where should this log file be?

Default logs in .minecraft\logs are only generated on startup.
This is what i see after world loading attempt:

Don't mind it, the problem was More Plates mod.
It removes all items from tags but its own.