Yea, this is currently not supported because of the way that Metadata is currently stored. We do know of this shortfall but haven’t been able to design a suitable solution to it yet.
We are planning on refactoring the Linking screen later this year which will include the abiltiy to report on assets that are linked to metadata fields.
We also need to do the same for Safe Trash checking, to make sure that when that’s on, you can’t delete assets that have ID references to related metadata fields or values in WYSIWYG metadata fields.