Can you use silicon sealant for car quarter window?

You mean SILICONE, dumbass. Silicon is a hard crystalline substance that computer chips are made from.

FAIL

Yes. Usually they use soft sealant, but RTV will work.

If it is to seal a gap and not to hold anything, you can buy a low viscosity silicone that will flow into the gap. I have only used it once, to seal under a glass shower door, and can't remember where I bought it. Probably at a hardware store.

The normal stuff will just make a mess.

It's YOUR car. You can do anything you want with it.

You "can" use whatever you want.

But it's not the proper way of sealing automotive glass.

RTV works good and holds up for a couple of years before UV rays deteriorate it.

Absolutely not.

The version sold for bathrooms and aquariums gives off acetic acid (vinegar) as it cures. Put that into contact with car paint and a steel bodyshell and it will soften the paint and corrode the steel to make it rusty. It won’t happen immediately as it’s a weak acid, but the silicone rubber and the window rubber will have trapped it in contact with those surfaces where it can remain active for a very long time.

The only silicone sealants which are safe to use are the more expensive versions which are specifically designed for automotive use so will not damage paint and steel.

The above assunes the window is set into a rubber surround. No silicone sealant is suitable for glass which is directly bonded to the car bodyshell. That requires a special bonding agent and ideally a UV light to set the bond, but direct bright sunlight will also do the job far more slowly. The car must not be used during the bonding process as it causes the bodyshell to flex and ruin the bond.

no ..its not recommended and is not strong enough