No. Actually, you didn't. You couldn't have, because it's not a supported CPU.
I mean, technically they could have read that at someplace that was listing incorrect information. I wouldn't be surprised if somewhere on the Internet, someone wrote that 5000-series processors would work on that board.
And of course, even the official product page for that board suggests things like
"The AMD A320 chipset delivers outstanding capabilities for the latest AMD AM4-socket Ryzen processors", which might have been true when the page was last updated, but isn't actually true now. There could also be some confusion between "3rd-gen Ryzen" and "Zen 3", which the 5000-series processors utilize.
And it probably doesn't help that the official product page and specifications page for the board don't appear to even link directly to the supported CPU list, instead suggesting that one should
"* Refer to www.asus.com for CPU support list". Never mind that the page is already on asus.com. Kind of a poor site design there.
I did see the amd ryzen 7 5700X listed in the CPUs for this MB. I tried it and it did NOT work. Please advise what CPU WILL work with what I have? I also need PCIe 4.0 support for my SSD.
There is no 5700X, at least not currently, as the only 8-core 5000-series retail desktop processor without integrated graphics is called the "5800X". You might have seen the "3700X" listed, which was the previous-year's 8-core, 16-thread part. That might be a decent option if you can find one priced lower than a 5700G, as even that should perform around twice as fast as your A12 processor at most CPU-limited tasks, and is only around 10% or so behind the 5700G. It doesn't have integrated graphics though, so knowing whether you need those would be helpful, along with what you intend to use the system for. You might not even see much benefit from going with an 8-core 16-thread processor depending on what software you are using, so fewer cores might potentially work just as well for your needs.
As for processors with integrated graphics that would work in your existing motherboard, the 3400G was mentioned, but it only has half the cores and threads of those other processors, with each core being a bit slower too. It would still be a notable upgrade over an A12-9800E though. That is, assuming you can find one in-stock near its retail price, which should be $150 in the US, but the processor is out-of-stock at all major online retailers here, and is marked up to much higher prices by resellers.
Of course, none of these options would provide you with PCIe 4.0. To get that, you would need to switch to a B550 or X570 motherboard, and get one of the Ryzen 3000 or 5000-series processors without integrated graphics. However, you might not even see any significant benefit from PCIe 4.0. It technically allows for up to double the maximum transfer rates of PCIe 3.0, though in terms of real-world application performance, you are unlikely to notice any difference compared to running the drive at 3.0 speeds, as for most file accesses, other components in a system will be what's limiting performance with these fast drives. Only when copying large files or running a synthetic benchmark are you likely to see any difference.