According to officiel AMD Specifications, both the AMD Ryzen™ 7 7840U and the AMD Ryzen™ 7 7840HS do support DDR5 ECC RAM with the FP7r2 Slot.
Today the Bedrock R7000 was unveiled which officially supports DDR5 ECC RAM along with the 7840u, which means, that it is absolutely possible:
If the Framework 13 and 16 do support ECC with the AMD CPUs I would order at least 5 of each.