A similar one exists for the % of stocks trading above their 50-day MA. TradingView has that symbol / breadth indicator as well, so check it out.
The upshot here is that as SPX has made a series of 4 higher highs, breadth has deteriorated starkly, carving out a series of 4 lower highs.
Notice how much breadth worsened as well on 5/24/23 (last red candle shown at the far right of the upper chart). Breadth has fallen from near 50% of SPX stocks > 20-day MA to now being only 35.3% of stocks > 20-day MA. This shows what we all know already—the market has been unhealthy with only a few tech stocks holding up all indices. This points to the liquidity issues that affect the weaker stocks first.