Soldered RAM is soldered RAM — ECC doesn't matter.

No. ECC or not, if the RAM is soldered, you cannot upgrade it. Period.

The upgrade process is the same: you can’t. Soldered RAM is fixed to the motherboard. Whether it’s ECC or non-ECC, your only “upgrade” option is buying a different machine. ECC adds error correction, not a magical upgrade path.

The real question is whether soldered RAM is the right choice for your needs — not what flavor of error-checking it has. If you need upgradable RAM, avoid soldered entirely. ECC is irrelevant here.