Because the movie was filmed in the IMAX format in some scenes while other scenes with the regular format (with black horizontal stripes).
This are the technical details: Aspect Ratio 1.43:1 (some scenes: IMAX 70 mm and Laser). And no it doesn't affect the story.
Armed with only the word "Tenet," and fighting for the survival of the entire world, CIA operative, The Protagonist, journeys through a twilight world of international espionage on a global mission that unfolds beyond real time.
What was the budget for Tenet?
$205 million
How much did Tenet earn at the worldwide box office?