There is a lot of misinformation about B550 as it was thought at one point to not have PCIe 4.
With it being so new a lot of this bad info and speculation is still around.
From the front page of the same website you quote right now is a review of the ASRock B550 Taichi.
“The B550 chipset has less PCIe 4.0 support than X570, with only the top full-length PCIe slot and one PCIe M.2 slot operating at PCIe 4.0”
Thus the older information you seem to have is incorrect.
Whilst it is not an exclusively PCIe4 board, the things that matter are covered with PCIe4, being GPU and storage. and the real world benefits of either are questionable at current, but it’s still wise to buy into an up to date platform.
Also the block diagrams from AMD themselves show PCIe 4, and it’s advertised on their website.
https://www.amd.com/en/chipsets/b550
Also note this board from Asus (a random example)…
https://www.asus.com/Motherboards/ROG-STRIX-B550-E-GAMING/
Clearly shows PCIe4 to the first x16 slot and to the first M.2 slot.
B550 boards absolutely and without argument have PCIe 4.0 they are out there and this information is accurate and real and current.
The B550 boards are in fact so ■■■■ good they almost make X570 redundant.
All except one thing, the price, and I’ve mentioned this a few times.
The are newer than the X570, only being released a few months ago, but at launch they were stupidly priced, hence why i myself have an X570 board (it was cheaper than a B550!!!).
Price being equal I’d recommend X570, B550 being cheaper (and it is coming down in price) then B550 will start to make sense.
Here, now today it could go either way, for $10-$20 difference the slightly older but higher end X570 could well be worth the extra, or if it saves $20-$30 or more then the newer B550 is the go.
There might also be some confusion over slots vs lanes, only one of the PCIe slots is gen 4 (with 16 lanes), but that’s more than enough for a single GPU setup, and with SLI and it’s cousins being all but dead no one is going to care too much.
–And if you have money for dual RTX3090’s then saving $0 to $60 on a motherboard is the least of your concerns.
Something to remember, the PCIe lanes in question don’t even come from the chipset.
They come from the CPU, hence why it was also thought that X470 and B450 boards running PCIe4 capable CPUs might get PCIe4 support.
Problem was that the physical lanes on the motherboard need to be designed to a higher standard to ensure the signal integrity required for the faster speed.
It was decided that adding PCIe4 support to those boards could potentially lead to reliability issues as the boards were never originally designed for it.
The reality is in 99% of cases it would have worked flawlessly, but AMD erred on the side of caution and did not retroactively activate PCIe4 on said boards, a wise choice in my opinion.
Given the guesswork pre launch and how new the chipset is it’s easy to find plenty of speculation and bad info. I have a lot of respect for Anandtech, a great place for info, they got it wrong, but even so they’re usually a better source than most in my opinion.
-A little regarding storage bandwidth.
See the NVMe vs SATA ssd video i posted above re game loading times.
SATA 3.0+ being 600MB/s and PCIe3.0x4lanes being 3,940MB/s you’d expect NVME to be >6.5x faster.
In benchmarks the difference is staggering, in reality the difference is so small it can’t be noticed.
We’re talking double the price for a drive for a 1-2 second load time benefit.
In my option I’d say the money is better spent on a larger SSD than a faster SSD as long as it at least has DRAM cache.
My Samsung 950Pro which will bench 3.5GB/s and my Intel 540s with does 1/6th that speed both have load times for MSFS within about 1-2 seconds of each other.
And according to disk bandwidth and access time data MSFS is not starved for bandwidth with either disk.
So assuming you’re not running a trash SSD, SSHD or a mechanical drive there is nothing to be gained real world for FS2020. In my private testing the evidence is just not there.
A little side bit, should have got the 3700X 
Not overclocking is not a reason to avoid that chip, gives you a higher clock and 2 extra cores than the 3600. That said i don’t know what the market was like when you bought, the 3700X has dropped in price considerably over the last few months, might have been pricey when you built.
At this time I’d consider it the #1 choice for MSFS in the mid range price point.
The 3600X and 3800X are pointless and shouldn’t exist… says me with a 3800X…lol.
Crazy sale or something, got it for the price of a 3600X at the time!!! AUD$424 delivered (~USD$305).
But seriously, only chips to consider for sim and gaming are 3600, 3700X and maybe 3900X (and the XT variants.
For multi threaded friendly workloads the 3950X cpu can be a valid choice also.
No argument intended, just the information i was seeing looked wrong.
If there is better evidence I’m open to being corrected.
Also just found this slide from AMD the covers the current 500 series chipset range.
The A520 will be on shelves soon… probably a great budget chipset, but i have no interest in it really.
Might suit office or web surfing tasks well into the future, but the entire lack of PCIe4 rules it out for me.