Did it get sealed right after it was installed?

Have you re-sealed it at all since it was installed?

Unfortunately a common occurrence with the "white" or light gray quartzites.

It was sealed upon installation but we have not gotten it resealed. If it gets resealed is there a potential it can “dry” ?

Are you sure it's really quartzite and not marble? Lots of stone yards mislabel marble as granite or quartzite. Quartzite is quite dense so it doesn't usually absorb liquid.

I'd find a stone restorer and ask their opinion on how to address the problem. Your fabricator probably doesn't want to deal with problems after installation.

If it was installed in 2022, and started staining 18-24 months after install... is it safe to assume it's been stained for about a several months to a year now? What is your warranty from the fabricator? And how long have you been trying to get a hold of the fabricator?

I cannot imagine the fabricator is in any way responsible and what is causing the stains ? If it was sealed on install were you told to reasel yearly ? Often thta is a must. I also agree it might be marble but really the resealing was up to you.. I have to say I do not see the stains well so but are they all over or just around the sink ?