Analyzing the keyword "how to get more Google reviews" under the Top 10 Benchmarking tab in the On Page SEO Checker tool you can see that a Featured Snippet can be triggered by this keyword (see the picture below). But there is no information about this in the SERP Features Ideas section of the Optimization Ideas tab. How is this possible?

The On Page SEO Checker's "SERP Features Ideas" section specifically provides optimization suggestions for your page. If your page isn't ranking in the top 10 for a given keyword, Semrush won't offer ideas for how your page can capture a Featured Snippet for that keyword, even if a Featured Snippet exists for it. The "Top 10 Benchmarking" tab, however, shows what SERP features are present for the keyword generally, regardless of your page's ranking. Keyword Volume is not a direct factor for whether a SERP Feature Idea appears, nor is the number of Referring Domains.