Yeah that x570 board you have doens’t appear to have support for x16 x8, sadly. I wish it could, that would be amazing. I have been looking for something like you’re talking about for a while, and others have too. I haven’t found anything of the sort out there, sadly. Here is another post with a search extremely similar to yours: AM5 Motherboard with no Gen 5 M.2
It could be done with x16 and x8, but in that case you must sacrifice any nvme drives to the chipset.