I'll answer the OPs question by explaining what inversion is, because I understood it perfectly. You see, you understand what inversion is by thinking about how you would use it in your own life, if you could. If I could invert entropy, then the only thing I'd want to invert is my decision to hand over my hard earned $16 and my decision to spend 2.5 hours of my life that I will never get back, in exchange for sitting through this pile of utter rubbish
Seriously though let's set aside all the time travel bullshyt. That's not what makes the movie so terrible. I can deal with a complicated movie that is about far out concepts that take a lot of time to understand. That's not a problem.
The reason it's the worst thing I've ever seen is because literally none of it matters to the viewer at all. "The world is going to end because of the Russian guy" - WHO CARES, I want the world to end so that I don't have to suffer through another second of these completely robotic characters with zero trace of humanity to them at all. No backstory, no emotions, no passions, no virtues, no skills, no weaknesses, no relationships, NO god damn names... nothing. fukk me dead, even porn movies have better character development than Tenet did. When I watch a porn film, I care about the woman because I want to bust my nut in her, because she is a human and an attractive looking human at that who fools my reptile brain into thinking she might actually be a good mother for my children because she's got wide hips and huge breasts. When I watch Tenet, I don't give a shyt about any of the characters or what happens to them, because there is zero character development. They're not humans. There's nothing remotely human about them. They're not even robots, because I've seen movies with robots in them (like I, Robot with Will Smith, or Blade Runner), and even the robots have deeper characters than the so-called human characters of Tenet.
So yes, I stand by what I said, the average porn video is better movie and a better piece of artwork than Tenet, because it is able to arouse feelings of investment into the plot and feelings of care towards the characters, which Tenet is completely unable to do at any point in the story.