You may be confusing CES with some other organization. I asked on CES's public discord:
ranicki: someone on HN claimed that Center for Election Science switched from pushing STAR to pushing approval. is it true that this organization formerly supported STAR, or was it one of the other organizations? I don't remember who was advocating for what
-redacted name-: Center for Election Science has broadly supported cardinal voting methods, score voting and approval voting basically since its inception. From everything I can tell it still is supportive of cardinal methods broadly, but as a political tactic has honed in on approval voting specifically due to its Pareto optimality.
...
-redacted name 2-: I don't think CES ever changed from STAR to approval. IIRC they existed long before STAR was invented
(Names are redacted because I didn't ask permission to quote, but the discussion is publicly visible and not sensitive at all.)