This is (slightly) wrong. ALL Socket AM4 Ryzen CPUs without an iGPU have working ECC support.
ONLY AM4 Ryzen APUs (i.e., CPUs with an iGPU) with the "PRO" infix in their name have working ECC support.
However, ALL AM4 platform ECC support also depends on the motherboard vendor/firmware. There are boards on which ECC simply will not work, no matter if your CPU and DIMM combination actually supports it. You have to check the mobo specsheet to make sure it does - ASUS and ASRock, for example, support ECC on most of their boards with a suitable selection of CPU/APU and DIMM.
To illustrate the CPU situation with a few examples:
- Ryzen 5 3600 - proper, working ECC support possible.
- Ryzen 7 5800X - proper, working ECC support possible.
- Ryzen 9 3900X - proper, working ECC support possible.
- Ryzen 5 5600G - no ECC support possible.
- Ryzen 7 5700G - no ECC support possible.
- Ryzen 5 PRO 5650G - proper, working ECC support possible.
- Ryzen 7 PRO 4750G - proper, working ECC support possible.
Apparently this might be specific to AM4 iGPU models?
I've seen suggestions that for PRO, the memory controllers were redone. Wouldn't surprise me if the story is that Cezanne had a design error resulting in inoperational ECC, especially given that unlike done other models in the series they are not chiplet based.
ONLY AM4 Ryzen APUs (i.e., CPUs with an iGPU) with the "PRO" infix in their name have working ECC support.
However, ALL AM4 platform ECC support also depends on the motherboard vendor/firmware. There are boards on which ECC simply will not work, no matter if your CPU and DIMM combination actually supports it. You have to check the mobo specsheet to make sure it does - ASUS and ASRock, for example, support ECC on most of their boards with a suitable selection of CPU/APU and DIMM.
To illustrate the CPU situation with a few examples: