Using ASRock X570 PG 4S + Ryzen 5 2600 + Kingston 32GB 2666 ECC(cpu/mem support list for this mobo says the ECC works in this config). Dmidecode still reports 128bit data width instead of 72 however it also reports multi-bit correction instead of single-bit so ... ;). I'm kind of used to 72bit on Intel boards with UDIMM for example Supermicro+Xeon that I have. I think that a combination of memory controller plus mobo reporting has an effect on that info instead of actual hardware support - but still EDAC works, registers proper driver and I get the warnings once in a while from EDAC/RAS that a correctable error has been indeed corrected. Now if I should question whether it actually corrects something then I should also question the Supermicro+Xeon config - I don't have any means to check that - however if it's not working then I should see that on the ZFS dataset every month or so during scrubbing and I don't see anything there. So for me it is settled.