It's not going to be 7 months long... don't know where you got that info.
Believe what you want, not interested in debating this. On social media a while back a few crew members were found saying that they were scheduled to be in production on the film up to December. They've already been in principal photography on Tenet for 2 months, and have only filmed in 2 countries so far, and are only just now gearing up for the 3rd country.
Also the official press release mentions they will film in 7 countries. Nolan's not going to film in 7 countries in 4 months. This wouldn't be the first Nolan film with such a long production schedule. The Dark Knight had principal photography for 7 months, filmed in 3 countries. The Dark Knight Rises had principal photography for 6 months, filmed in 4 countries. Inception had principal photography in 5 months and filmed in 6 countries. With Inception, that is still one country less though than where Tenet will be filmed.
Lol. Nolan (and I) just proved you wrong... With Denmark shooting today, and India also in September, Nolan shot in 7 countries in 4 months.