What ended up working:

var shadowParent = driver.FindElement(By.CssSelector("macroponent-abc123"));
var shadowRoot = shadowParent.GetShadowRoot();

var somethingInsideShadowRoot = shadowRoot.FindElement(By.CssSelector("table"));

I had to wrap my head around shadow DOM and its purposes on websites, then I was able to get it sorted out. Thanks to Rahul for pointing me in the right direction!