We agree - Embodied Carbon is definitely in Scope 3 for architecture firms, and operational carbon might also be (we certainly feel responsible for it, anyway!)
From the GHG Protocol - " A scope 3 inventory enables companies to identify their downstream hot spots so that they can credibly engage with customers to reduce their value chain emissions."
Since we (as architects) deliver buildings to our customers, to me that says operational carbon would be a downstream hotspot, where we have the responsibility to engage with our customers to reduce the associated [scope 3] emissions.