Lack of character backstory is the whole point
The biggest argument against Tenet except for being confused that I see is the lack of backstory In the characters and that you can’t feel invested.
I hate this because this is the whole point of the movie. The main character is even called the protagonist to show that his story doesn’t matter, or that it would matter too much. You’re not meant to have a backstory. It defeats the purpose otherwise.
I know this will sound “douchey” but I feel Tenet is more a work of art than a movie. Let’s not even mention how they aced the backward/forward plot. Yes, it’s confusing but it all tracks perfectly if you watch it back including with the score. That must have been painstakingly hard to do. Of course, you can find some plot holes but this happens with every time travel movie.
But to get back to the topic of how we don’t know enough about the characters. This movie wouldn’t work with the plot if we did. The characters can’t know much about the others or it would open them up to be compromised by the future. And as we are brought through the story through what the protagonist knows so can’t we. I think this is truly masterful filmmaking.
Imagine this was a Terminatorish plot and we know the protagonist of the future and how he set everything in motion. This would lose the whole impact of what’s revealed. How Kat been jealous of the lady diving in the water was a wow moment. Watching back on scenes and noticing you see what happens at the end in Stalsk-12 without knowing is just great. The amount of detail that’s has gone into this where 90% of viewers won’t even notice is astonishing. Even people looking for these types of scenes need multiple viewings.
Admittedly it might not be a casual viewer’s cup of tea. For them the movie tells you how to watch it “don’t try to understand it. Feel it.”. If you do this I think it can be a very entertaining Nolan film. For others that do go down the rabbit hole. You not alone can find something new each time. It’s truly thought-provoking on time travel and even if events were predetermined, “it’s not an excuse for doing nothing”.