Have you tried soft scrub? This was recommended by my installer and did very well cleaning my off-white quartz counters.

No, will try that. Thanks!

What brand are your countertops? Did you find a solution? I have Caesarstone Noble Gray and am having the same problem. It is about a year after they were first installed and I feel like the problem is getting worse - I think it might be caused by water rings or possibly plates with oil on the bottom but really I keep things wiped up and only leave dirty dishes on the counter briefly. I have a couple of grayish rings - a little bit darker gray than the light gray countertops and duller looking - and when I use quartz cleaner OR Soft Scrub cleanser OR Barkeepers Friend (very judiciously) the rings sort of widen out to be smudgier rings or sometimes splotches as if whatever it is is spreading out from the original ring. SOMETIMES they go away on their own after a few months. After they have aged a bit I can sometimes scrape little bits of the rings (i.e. leave some trails through the rings) with my fingernails but don't want to use anything abrasive - someone suggested 0000 steel wool and I tried that but no effect. I have read that acetone removes some smudges, with a razor blade if needed, but I am reluctant to try these things as I don't want to make it worse. I have an email to Caesarstone about this but I have heard their customer service is not the greatest so am not feeling confident that they will help. The rings and smudges are only apparent in the sunlight. I also tried baking soda and it did not work but did not try leaving it on as poultice (with plastic wrap taped on top) overnight or whatever the advice is. Very frustrating.