History

Do you mean humanoid giants? Or dinosaurs?

No, there isn’t.

Personally I think it's highly likely that many different transient forms of hominids existed in the geologically-very-recent past. We have modern-day pygmies, we have the "hobbits" with the very surprising result that accurate information about them seems to still be a part of the oral history of some of the local aborigines. It seems highly likely to me that "giants" as in much-bigger-than-us hominids in some form or other existed at one point. Hell, depending on your definition they still do, e.g. the village of abnormally-tall men that Redmond O'Hanlon talked about visiting in "No Mercy."

That said, I think that the people you're thinking of who talk about "giants" are probably just making up nonsense or reading it on the internet. It's the same relationship as the genuine fact "pharmaceutical companies are not at all your friends" has with the claim that you shouldn't take the COVID vaccine.

There's also this, although I make no claim for the authenticity of that story.