https://github.com/stevearc/conform.nvim/blame/328c2f1dda56f933d3337a1316e1020ba30ba6aa/lua/conform/init.lua#L718
In this line config is defined as nil. If inherit is false then the entire if condition is skipped and formatter will be broken.
I consider this a bug since inherit=false basically acts as a red button for any formatter, and not as a definer of new ones.