Quick read about what what CPU is compatible with what motherboard then selecting memory and sufficient power supply.
You have 6 main components.
-Case
-Power supply
-Memory
-CPU
-Motherboard
-Hard Drive
I'm really surprised someone on HN would feel like it is a challenge.
* making sure the motherboard supports the CPU via socket and also nominally
* making sure the heatsink can be mounted on top of the CPU socket
* having the case fit your motherboard form factor
* if there is a dedicated GPU, making sure it fits inside the case and there is a PCI-E slot with sufficient lanes for it
* if not, making sure there is an integrated GPU
* selecting a PSU that can handle the maximum power load for the GPU and that has a power cable for the GPU if it needs one
* making sure to buy the right type of ram in accordance with what the CPU and motherboard support
* if you want wifi, making sure there is built-in or there is a m.2 slot for wifi
* if you want a m.2 NVMe SSD, there should be a m.2 slot with the right key interface
Not often you end up buying parts that don't work well with each other and need to buy other parts. I once bought a small factor m.2 ssd only to discover it didn't fit the slot. I think it was trying to fit an M key device into a B key slot. Sometimes even the vendor data can be incorrect.
It's really not necessarily that hard -- I say this not as an insult, but as an encouraging clue that whatever documentation or technique you followed last time you tried may have been overcomplicating things -- it can be about as easy as putting legos together.
So, if building your own PC from off the shelf parts (which is quite different from what the poster is talking about actually) is something that interests you, I would strongly recommend not giving up and assuming that it's too hard for you, and instead concluding that whatever resources you used last time to guide you are inadequate or aimed at a more complex goal than you need.
I can't give a specific recommendation since I haven't done it in years, but you really just need to pick out a case (which usually will include a power supply), motherboard, CPU, RAM, and hard disk. To make it easier, avoid needing a CPU and just get a motherboard that includes the CPU. (Same goes for GPU) Then, ensure the motherboard is compatible with the case, the RAM is compatible with the motherboard, and the hard disk is compatible with the motherboard. Finally, total the power usage for each component and ensure it's less than the power supply's power output. Honestly, this compatibility planning is the "hard" part, once you get the components it's just plugging them into each other in a logical way, it's not like decades ago where you had to fiddle with jumper switches and the like. For your first time, you can also just set your expectations low, make sure you get things with good return policies, and return components if you end up being mistaken about their compatibility, but this should not be an issue if you read their specs carefully.
You can even buy kits that already include parts known to be compatible. Or for example, bundles that include the motherboard and some compatible RAM -- if you get one of those all you really need is the case and you're done (Since technically, the hard drive is sort of optional, if you always boot from a live USB or netboot image!)
NewEgg.com used to be great for this kinda stuff years ago, although I've heard they've "gone downhill"? No idea
Or even further towards ease, take apart your PC and put it back together.
That said, lol, you're right, this is something for most people you do once, and it was cool, but next time you just buy off the shelf to save time. There was a time when you could save a lot of money building your own but that time is long past.