Can ETFs change their holdings?

ETFs can change holdings for several reasons. Index ETFs update when the underlying index rebalances or changes constituents. Active ETFs change holdings as managers make decisions based on their strategy. (sec.gov)

Even "plain" index ETFs can change more than people expect, especially sector or factor ETFs where reconstitution rules lead to turnover. Bond ETFs can also change frequently because bonds mature and indices roll.

If you care about stability, look at the ETF's turnover rate, its index methodology (if applicable), and how often it reports holdings. That gives you a better feel for how "set and forget" it really is.