SPX bounced from March'21 open (3812) which act as strong SR zone. Next is 2021 Year open at ~3764 (even stronger SR).
These two levels make this area very good one for consolidation and relief bounce. Another factor - chart completed 3-4 impulse waves which usually is enough for either consolidation of correction.
But this is all in theory. At that moment I don't see any confirmation that downtrend is over. Want to see SPX price to grow above 3985 and find acceptance there for beginning.