In the end it’s up to you, which makes sense, since you’ll be using the PC.
I’m just happy to see you’re actually making an effort to delve into the details before making a decision.
Regarding AMD CPU’s; they’ve been rock solid for years. I don’t know where your information about ‘crashing more’ comes from, but especially for the CPU side, that’s not correct. AMD CPU’s have been mainstream for years now, and have been recommended by experts in the field for years.
About AMD GPU’s; there were some driver problems when the Radeon RX5700XT’s initially launched. Some people suffered from those, some didn’t. But as is the way of things, the people with issues voiced them (and rightfully so). Since then (I think about 2 months after release) those driver issues have been resolved. I’ve had 0 problems with the drivers personally.
For the RX6000 series we won’t know for sure until they’re officially released, and thoroughly tested. I can understand you might be hesitant. Best thing is to wait for release and testing (both third party experts and the community in general). If you’re in a hurry (and actually can get hold of one) I would understand not wanting to wait for that and going with an RTX 3000 series card. Those will do fine.
About more cores working better for MSFS; I haven’t seen any proof of that at all so far, as long as you have more than 4C/8T. This might change in the future, who knows, but I’m not betting on it. You can always go with a 8C/16T part if you want to be sure.
Both Intel and AMD have offerings for those.
Here’s a screenshot from some benchmarks Linus Tech Tips ran, all Ryzen 5000 parts perform very similar (and all outperform even the 10900K, even on the 1% minimums (the microstutters):
source: Remember this day… - AMD Ryzen 5000 Series - YouTube
Anyways, I just wanted to assist you in having all information available to you before you make your choice, instead of disregarding AMD of the mark 
Both options will most likely perform quite well, it’s up to your budget and the price/performance available to you.
I also wanted to point out that the old saying of ‘intel is better for gaming’ is not true anymore.
Whichever you end up picking, I’m sure you’ll enjoy it.