Gonna risk stepping on a few toes here but sorry I don't agree with the rationale of "B550 is good enough for 5600X".
Motherboard is about features. Saying a cheap motherboard goes with a cheap processor is missing the point. All Zen 3 chips offer the same features. The only difference between R5/7/9 is number of cores, number of chiplet dies (doesn't matter below R9) and TDP. All these have little to do with motherboard unless you are building a system purely for pushing limits. I daresay even a A520 board will run the 5900X just fine out of the box.
Now to the motherboard. äøåé±äøåč“§, you get what you pay for. And pay for what you need, otherwise you will end up paying more in the future. One very simple example: many low end boards offer only wireless AC while most mid-end and above today offer wireless AX. You can get AC today but one day when you want to upgrade to AX, it's an extra $30 - $45. Then so many other things:
- how many PCIe lanes does it have and at what bandwidth? Nowadays with M.2 SSD becoming more common, this is becoming more important. PCIe lanes are shared with SATA and GPU also
- what kind/how many internal I/O headers does it have? E.g. USB 3.0, USB type-C
- how many fan headers does it have? It can mean the difference between buying additional fan splitters/hub, which will set you back anywhere between $10 - $50 all in.
- what kind of on board cooling does it have? E.g. VRM, M.2, etc
- what rear panel I/O does it have?
- does it have clear CMOS/BIOS flashback button? You may think this is nothing but it can mean the difference between saving your ass and bringing the board in for servicing when some settings go awry
- what onboard networking/audio chipset does it have?
- do you like the BIOS?
- what accessories does it have? E.g. some have cheapo antenna (I'm looking at Asus) while others have better build quality (Gigabyte is good)
- what are the placement of the ports? Is it going to be a problem for installation in your choice of casing?
- is it compatible with your choice of CPU cooler? Some boards have non-standard backplates or components on the back side that interfere with 3rd party installation bracket.
- etc etc etc
The CPU is just the engine of the car, so to speak. The car is a lot more than just the engine. As I mentioned in the Ryzen 5000 thread, not all mobo are created equal, even with the same chipset. Why does AsRock make two B550 boards for example (M vs. Phantom Gaming) So yeah it's really too superficial to say "cheap CPU get cheap mobo". After all, apart from core count and TDP, the 5600X also offers everything that the 5950X does. You save a couple $100 now, but after you upgrade here and there, add this add that, may end up spending even more than getting a good mobo from the start. If you have already chosen the mobo, then this is a done deal but for those who are still shopping, do give more consideration.