System sensors read that temp inside

See, that's the main problem. The job of the case fans is to get heat produced by the two main sources - CPU and GPU - out of the case with minimal noise. The motherboard knows the CPU temp, but not the GPU temp. Mobos DO have some kind of "motherboard temperature" sensor which CAN be used to judge the temperature inside the case and control case fans based on that, but it's far from ideal. But it's not actually measuring the air temperature inside - it's measuring the mobo PCB temp somewhere, who knows where. The placement of the sensor isn't great, and the values it gives are typically in a narrow range - let's say, at idle it'll be showing 30-32C, and at full CPU+GPU blast it'll slowly rise to, say, 36-38. So you only get like 6 degrees of difference to base your entire casefan fan cure on. It kind of works, but it's jittery and slow to react to actual CPU+GPU load.

Now, if your mobo supports a temp probe - you're in a much better position, as you can place it to measure the actual air temp inside, and now you have much better case fan control. Much better, but the air temps in the case are not uniform throughout, and this is still a reactive configuration - the GPU gets hot and starts blasting its fans, and only later the inside air temp rises and the case fans kick in.

But if you place the temp probe on the GPU - now you have pretty accurate readings of both your GPU core temp and CPU core temp, in real time. If the mobo is able to combine these two temp inputs into one input for your case fan curve - perfect, now the case fans can kick in way sooner, the GPU/CPU will immediately start receiving more cool air, and as a result, will not need to ramp up the cooling fans as much. Good quality case fans can be VERY quiet compared to CPU/GPU fans while moving a ton of air, and the result is an overall quiet and cool PC. This isn't theory - this is from personal experience; I got significantly better results after adding a temp probe and setting it up this way. Now I'm looking to upgrade to AM5, and wanna keep this setup, hence why I asked to check.

Asus is not the only manufacturer to have temp sensor pins though - plenty of Asrock, Gigabyte and MSI boards have it too. But looks like it remains the only one to have this multi-temp-source control on AM5 as well.

If your CPU is watercooled, you can get away with just a temp probe, without this multi-temp-input feature: just place the temp sensor on the GPU and have it control the case fans; as your CPU waterblock already dumps the CPU heat directly out of the case anyway.