This is the trap for new traders: an ETF that tracks an index is still a security, so its options are american-style-options that deliver shares. An index option on the same benchmark is cash settled and European. The exposure looks identical and the mechanics are not.
ETF options also pay distributions, so a short call that goes deep in-the-money before an ex-distribution date carries real early-assignment risk.
Example: two traders both want 12 months of downside protection on a broad US equity exposure. One buys an index put and can never be assigned. The other buys an ETF put on the same index and, if they had sold it instead, could be assigned 100 ETF shares at any moment. Same view, different plumbing.
Related: index-option, equity-option, xsp, early-assignment