Brand new shower drain smells like sewer

I moved into a brand new house last year and already the master bathroom shower drain has sewer smells to the extent I can smell it in the bedroom. When I remove the drain cover I can see water in the pipe. The drain cover is not screwed into any assembly, just sits on top, there is blackish/brownish gunk where the drain cover sits. The construction plumber just says too bad, but it doesn't seem like a shower should stink before a year when only one person uses it 3-4 times a week. Is there a better shower drain I could install? Thanks so much, KJ

Sounds like a vent problem or trap problem to me. Don't think it has anything to do with the shower drain itself. I may be wrong though.

The most common cause of sewer gas in a bathroom is a bad wax seal.

The smell is definitely in the shower since there is no smell after a shower, but it comes back after a few hours. I will sniff around the toilet to be sure. Then I'll clean the gunk off the shower drain and see what happens. If the smell is still there then it must be the piping, but I sure hope not.

Thanks so much for the help! I really appreciate it. KJ

something to check.
remove the strainer from the shower drain.

useing a tape measure, slowly insert it into the shower drain. when you feel it stop, push it , if it goes around a bend

and then gets easy to push. that is a 90 degree bend

if it seems just down right impossible to go around what ever the hell is down their...that is a p trap

finding a 90 is not good, finding the trap is good