For me it's when they stopped showing results that include your keywords and instead a random smattering of anything broadly related to the topic being searched for.
https://blog.google/products/search/how-were-improving-searc...
IIUC "verbatim mode" is supposed to do something like this. https://search.googleblog.com/2011/11/search-using-your-term...
For example, Google often prioritizes obscure music bands or albums even for generic or well-known terms.