This is the view out the northern window in my bathroom. My neighbor has been cleaning their yard for years, which has just involved them piling garbage in a trailer. The trailer has never been emptied, and At this point I doubt they could move it without the majority of the trash falling out.
Luckily the fence on that side of the yard is 6 feet, so I do not really see the trash under normal circumstances.
Came here for this, call housing code enforcement. If they exist where you are.
Alternatively, OP could try talking to their neighbor about it instead of getting the state involved. Maybe even offering to help them clean it up? Getting the authorities involved could cost the neighbor money or have bad repercussions and we don’t know what their circumstances are.