Even on regular AMD 7000 and 9000 series the DDR5 memory controller is very sensitive and hard to get a stable system with fast RAM on many motherboards when all 4 modules are present. At today's RAM speeds, I definitely think a stable soldered system is increasingly a better trade-off.
Indeed. I have an AMD 9950X and an Asus X870E* motherboard. I can barely get the system to boot with one 32G DIMM let alone 2 or 4, and 48G DIMMS are even worse for some reason. I have tried 3 different "matched" sets. Sometimes I have to reset the system 3 times or more before it will boot; it hangs or crashes on DDR timing BIOS codes. I have given up and just use a single 32G despite how useless 32G is in a high end desktop today. Real joke. Huge waste of money. I will buy prebiilt systems in the future. In the meantime if I need a lot of RAM I use an Intel 14900K desktop or my new HP G1a Zbook.
* ASUS X870E ROG CROSSHAIR HERO AMD AM5 ATX Motherboard
Yes, AM5 DDR5 support has been similarly painful to me on four systems (7950X and 9950X). Try forcing the memory speed down to 3600MHz (ouch) when you want to install lots of memory and stay on modules specified on the motherboard's QVL.
I'd probably go Framework Desktop next if I won't need peripherals.