Framework 13 related speculation here: Will the new AMD boards support ECC RAM?
Traces are absolutely needed between FP7r2 and the SO-DIMM slots. The parity data has to be transmitted on those traces to the memory controller in the CPU and is checked there. So no traces means 100% no ECC support as you say. Traces connected could still mean anything from fully working to not working at all.
I fear there will not be definitive “yes” answers on this topic since close to nobody will do validation for consumer products where there is no real pressure to do so. At least there are AMD desktop mainboards with functioning ECC support, even if it is not actually advertised as such. One example of that seems to be https://www.asrock.com/mb/AMD/X670E%20Steel%20Legend/index.asp#Specification as shown in https://www.reddit.com/r/Amd/comments/1114dpo/any_am5_motherboards_with_full_ecc_ddr5_memory/j8k40vf/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button.
Actually the specifications don’t explicitly talk about ECC support at all. “- Supports DDR5 non-ECC, un-buffered memory up to 7600+(OC)” is all you get, which interpreted to the letter just means that non-ECC will work but doesn’t say anything about what ECC will or won’t do.
Soooo: