Same, came to google after DDG failed to locate a string that I suspect would occur (error message on Factorio forums). Google then gives me some LLM hallucinations about what the error might indicate, also when you specifically don't click the "use AI mode" button (that the search button automatically turns into) but the "search" button. You don't get any search results whatsoever. After it started wasting energy on hallucinations, you're allowed to click "all", meaning "web search, please" (should be obvious to anyone)

Why in the world would it specifically do this for site:https://example.org "exact string" queries?! I know what I'm looking for and where it can be found!

It's like redirecting my phone call from ISP support to a librarian because maybe the library contains the answer to a dysfunctional SIM card they've sent me

This still works for me: https://www.google.com/search?udm=web&tbs=li:1&q=site:reddit...

It seems they have been A/B testing killing search operators (like "site:" or "inurl:") for a while. They randomly stop working and switching to private mode, or the other way around, makes them work again.