My System (Ryzen 7 1700X ans Asus Prime X370-Pro, Power-Supply 750W) has all requirements, I own a Crossfire Cable, too.
Thank you and greetings from germany
You cannot crossfire those cards.
Sorry but this is likely not possible.
Also, you should give this video a watch for when you do get videocards that match up.
Why Don't Multiple GPUs Scale Properly? - YouTube
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