The yellowing in the quartz is the resin component of the material degrading. Is your sink in a sunny area? Sometimes light exposure is the culprit with quartz yellowing. Darker colors of quartz don't show the yellowing as badly. The solution is replacement, although you might try consulting a local refinisher to see if they have any professional solutions. This isn't something you'll be able to address with home remedies. Yellowing of quartz is one of the big reasons many consumers choose natural stone instead, to avoid the issues with the resin content of the quartz. I don't know what Zodiaq's warranty period is, but you could try looking into that.

Contact your fabricator to initiate a warranty claim.

If it’s just around the sink, could it be a reaction to the chemicals in whatever you are using to clean the sink? Do you have a picture?

Tear them out. Replace with good old reliable Formica. Not cheap pre-laminated particle board counters from the big box store, but custom made 3/4" plywood with Formica laminated on-site.

Formica isn't fashionable these days, but it lasts well, and it doesn't need to be babied like these expensive, fragile materials, some of which Formica replaced in the 1950s for good reasons.

Simply replace your sink with one with a larger footprint: