Yes it is shadercache as you wrote.
But just to prove I’m not totally crazy, I included an image showing it only says “Updating” above the progress bar. Which is why I thought it was the game that was updating.
But hovering the (i) it says “shader pre-caching update.”
Then there’s the question why it needs to update shader cache nearly every time I’ve played the game?
Nope, it only helps to not increase it further.