I’d call my landlord.
But if you want to try fixing it yourself go buy a 12’ section of the cheapest metal pipe you can find. Then buy one of the special street line plungers. They look like a cross between an upside down wine glass and a plunger. They are small enough to fit tightly down the access pipe in the front yard. Screw that onto the end of the pipe, secure it real well with some pipe clamps, and plunge the vent in your front yard. I know Hectors carries them because that’s where I got mine. Really slam that thing down there and the air pressure it creates in the pipe will clear anything but roots in the pipe. If roots are the problem a plumber will have to come use and auger to cut them out.
About a year after buying my house we had a backup in the line to the street. I called a plumber and he came out and did this, line opened right up. He suggested I build one of these plungers myself and for about $20 in parts it was a great investment. I’ve used it 2 or 3 times since.