One Source of Truth

Your app now has several pieces of state, and each of them lives in exactly one place: favorites and search in App. Every component that shows them gets them as props, and every change goes through a function that App passed down. That's what one source of truth means: each piece of data is stored once, and everything else is read or computed from it. When the user stars a band, the star, the header and the lineup change together, because they all come from the same favorites.

When you add a feature, ask three questions:

1. What does the user change? That's state.
2. Which components need it? The state goes into their closest common parent and comes down to them as props, with a function that changes it.
3. What can be worked out from what you already have? Compute it while rendering, don't store it.

A list can go through several filters, one after another. With let, the list starts as the result of one filter, and an if filters it again:

let shownBands = bands.filter((band) => band.stage === stage);
if (fridayOnly) {
    shownBands = shownBands.filter((band) => band.day === "Friday");
}

Sometimes, data has to go many levels down, through components that don't use it themselves and only pass it on. For that, React has context, which a component deep down can read without its parents passing it along. In apps the size of yours, props are simpler and clearer.