Sounds similar to recently launched buffer ETF products, specifically BlackRock and Innovator that hedge 100% of downside while capping your upside across different time horizons indexed to the S&P500.[1]
They don't guarantee you zero downside compared to investing in the index, though, but compared to putting your money under the mattress.
It's relatively easy to achieve a return profile like these promise with some combination of Treasuries and index options (at least while Treasuries pay 5%!), and the ETFs are doing this kind of financial engineering rather than promising to beat the market through stock-picking skill.
[1] https://www.bloomberg.com/news/articles/2024-07-01/blackrock...