I did... Again, plenty of reports and discussion about it online though, as previously stated, your mileage might vary. Results from Startpage are a carbon copy of Bing's for me. Bing struggles with a lot of queries in Portuguese whereas google does just fine so its incredibly easy for me to spot.
On another note, the ads you get being from Microsoft or Google is another tell. As Vlad has stated in community streams, both Google and Microsoft like to bundle their ads with their search results and Startpage clearly complies.
But... I have left the best for last. Startpage itself has now removed any mention about using results from Google in their updated support page regarding their sources: "Powered by partnerships with MapQuest, HERE Technologies, Priceline, OpenWeatherMaps, Search Expander, and Microsoft Bing, our updated search result experience brings you richer information in a clean and easy-to-use interface" - https://support.startpage.com/hc/en-us/articles/12727471498644-What-are-Startpage-s-enhanced-search-results
Clearly, looking at Startpage's social media channels, people prefer google results and Startpage certainly knows that, them having long insisted they were not phasing out google completely even as they are doing precisely that. Why would they then turn around and remove mentions of google if they were still intending to continue using it? That just doesn't make a any sense from a business standpoint
Some better research before insisting on misinformation seems warranted 😅