I wonder if this is Pseudoinonotus australiensis (previously in Inonotus, the change in 2022). I’ve seen it just once when I collected it in the Gloucester area of NSW. If you look at the GBIF results for this species (https://www.gbif.org/occurrence/search?taxon_key=2521228) you’ll see that they record only seven other collections, held at the Oslo fungarium. Of course there are probably more elsewhere that either don’t get into GBIF or are misidentified. When I collected mine I assumed it was a large Coltricia. Here (https://www.gbif.org/occurrence/4422619303) you can see a photo of an isotype collection. In this species the underside is not white when fresh and it doesn’t bleed red if you run your fingernail across it.