I use the graphql productUpdate mutation to update a product as well as the product variants and metafields.
In general this works as expected, I can update metafield values as I want to. But I run into problems when I want to reset a metafield, i.e. when I set the metafield value to null.
If a metafield value before was e.g. "Apple" and I want to set it to null, nothing happens, the value is still "Apple". If I try to set it to '' or ' ' it does not work either. '-' works, but it is not a pretty solution.
I also tried not including the metafield in the metafield list, but the value of the metafield is still "Apple".