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I've been using Presearch for a while and often forget I'm not on a common one. But when I really need something more obscure or hard to find due to most engines' algorhytms, I sometimes go for Yandex, which doesn't filter out most stuff Google, Bing,... do, but it leaves you filtering through a bunch of Russian stuff... 😅
My search-engine test for this is quite simple, though. Look for something specific nobody wants to see (like known scam sites like bitcoin doublers), there's plenty of those still around, but they usually are part of the great search-engine filters, so if I look for those specifically and find them first entry on a search engine, that usually means the engine results are not tweaked and I'll have more chance finding what I need rather than what it thinks I should find/need...