Steel studs, maybe?
Just get some good drywall anchors. Lots of options.

Could be concrete block.

There is also a building here with walls made of drywall layers with drywall strips in between to create a cavity wall set into a metal channel on the floor and on the ceiling plate. Very odd construction.

It would be more accurately named a density finder.

You shouldn’t be putting holes in a firewall. Command style hooks with lightweight objects only.

Could have two layers of type x drywall which would be firecode and would defeat a stud finder.

I wish it was a firewall. Given how shoddy the construction is, I doubt it. After moving in, it's clear that the walls were slapped together to divide the floor into apartments. It's not concrete either. I wish it was concrete.

I think Hallett & Co. and palimpsest are right about two layers of drywall. I just never expected it. Taking into account the replies, I'm going to use a combination of Command hooks and drywall anchors to hang jackets, bags and coats. Nothing too heavy. There goes the plan for the wall pot rack and the cork board I was hoping to install on the shared wall in the kitchen.

Thanks to everyone for replying. Now I know it's possible not to find studs.

It may be a good idea to get approval for what you want to do with the owner, or their representative, of the apartment.

Consider monkey hooks instead of command strips as they will hold a lot more weight. There are even ones for flushing mounting things-- useful for hanging objects that have a keyhole hanger on the back.

Have an outlet on that wall? You could take off the plate to take a look inside

I'd also check your electrical outlets and switches. Receptacles and switches need a box. Boxes have depth. You'll get info for anchors when you know the depth you have.

Is there drywall on the wall then there are studs how would the drywall get installed without them. How would you know if that wall is loadbearing and if you use the proper drywall anchors you can hang the things you want IMO for coats get coat stand .

Try using a strong magnet vs stud finder - also it may be double drywall as a fire stop required in some areas as others mention previously

Two sheets of drywall separated by acoustic caulk could be the construction method. That's a good thing.