I just built a system using the X13SCH-F board and the Pentium G7400 with 32GB of Micron 4800 UDIMM ECC in a single DIMM. TrueNas Scale is reporting ECC memory on the dashboard, but I can't find any mention of it in the bios. `dmidecode -t memory` reports single-bit ECC, but I don't see any references to it in logs.
The usual "Supports ECC RAM" line is completely missing from the ark page for the Pentium G7400 (as opposed to showing an explicit "No"), but the G7400E (embedded) ark page shows "yes" for ECC support. So I contacted Intel and....they have no idea if the G7400 supports ECC. They're going to get back to me in a few days after "consulting the engineers".
In the meantime, I'm incredibly impressed with the board's efficiency. With a Seasonic TX-700 (700W) PSU and a Samsung 870 EVO 500GB SATA SSD connected (boot disk), this build is idling at 18W measured at the wall. The PSU is 72.6% efficient at that 2% load, so about 30% (4.2W) is power-loss. If you assume another 3-4W for the BMI, the board+chipset+CPU is using around 10W at idle. (Where I live, electricity is $0.60/kWh so I'm highly motivated to keep things efficient.)