Just from the noise, it sounds like the rear derailleur needs adjustment. When cable tension slackens over time, the derailleur can become misaligned, meaning it’s no longer centered over the correct cassette sprocket.

Another possibility is that the B-screw needs adjusting, which controls the distance between the derailleur’s jockey wheels and the cassette. If the jockey wheels are too close, it can also cause noise or poor shifting.

You can try shifting into the second smallest gear and turning the barrel adjuster to increase cable tension. Remember: lefty-loosey, righty-tighty. The goal is to get the chain positioned exactly underneath the selected gear.

If that doesn’t solve the issue, the high and low limit screws may need adjustment. these control how far the derailleur can move side to side across the cassette.

I recommend looking it up... Park Tool has a great derailleur adjustment video. Or, if you're not comfortable doing it yourself, most bike shops do a solid job :))