XFX Radeon "True OC DX12" RX 460 2GB Single Fan (RX-460P2SFG5) supports bridgeless 2-way CrossFireX. Try each of the cards in each of the slots one at a time to confirm both the cards and both the slots work.
AMD Ryzen 3-1200 has 16xPCIe3 lanes, it should run x16 single-GPU or x8/x8 multi-GPU.
ASUS PRIME X370-PRO motherboard supports x16 single-GPU or x8/x8 multi-GPU. Manual is
here. You may need to explicitly configure PCIe lane settings or graphic output devices in BIOS. You may need to confirm onboard jumpers/switches for the PCIe slots are enabled.
Your PSU is sufficiently rated and has the necessary PCIE12V connectors for these cards, but there's
a lot of user reviews/complaints about it having a weak 12V rail which causes issues with high-end GPU or multi-GPU setups. Enough complaints (at enough different websites) that I'm inclined to suspect it's the issue - try a different PSU if nothing else seems to correct the problem. It's very telling that the PSU isn't officially rated for CFX or SLI ... these certifications are largely a formality because any PSU with the correct power outputs should work well enough, but the conspicuous lack of these certifications suggests a real lack of confidence in the product, lol, they're almost free to obtain and they're basically free advertising in a very competitive PSU market.
HWMonitor,
CPUID, and
GPU-Z are basically the best (free) monitoring tools available, preferred over whatever random wares WinOS, AMD, and XFX may have given you.
Games which aren't CFX compatible should still work fine - they'll just ignore the second GPU card.
But if you're running AMD Catalyst then you might need to change some software settings within it for best compatibility or best performance with certain games, basically don't mess around with what works and go hunting for solutions on the game support forums for what doesn't.
You may need to (re)install games and (re)update the games *after* you've got all your drivers and settings working properly. Focus on a game which uses single-GPU and a game which uses multi-GPU, make sure things work properly before installing the rest of your game library (just simplifies things and saves time).
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