Sorry, not a native English speaker, probably missused "not a thing". I thought it would mean "not important" or "not something people use all the time" or "irrelevant".

You wanted “not common”, sounds like.

“Not a thing” is a confusing idiom. It specifically means never happens, ever, but the idiom is frequently used in contexts where hyperbole is expected, so a literal translation accounting for the hyperbole might be something more like “I’ve seen it once, but it’s vanishingly rare”.