You can totally play it by yourself but everything takes tremendously longer with only a single person.

Enemies do have less HP when solo (+40% per additional player) but you will also not be able to play as aggressively or capitalise on stagger bonuses as frequently.

All aspects will just be slower than is possible with extra people.
Every person multiplies the number of goods that can be moved at a time, and portal linking requires more planning with only yourself to set up each end.