There's a brilliant WW1 film documentary, made by Peter Jackson, which used footage from WW1, colourised it and added sound effects and voice acting. Quite surreal and very well done. It used to be on BBC iPlayer, but isn't anymore. Just checked, and It is on Britbox, which you can sign up for a free one month trial.
The best WW2 documentary I've ever seen is The World at War. It was made in 1974, narrated by Laurence Olivier, and because it was made less than 30 years after the war ended, there were plenty of survivors interviewed, as well as tons of footage.
I remember watching at least some of it as a 12 year old when it first came out and the episode on the holocaust had a profound effect on me. I watched the whole series again a few years ago and it's superb.
It's currently free to watch on UKTV Play. There have been episodes on YouTube in the past, but you might not get all the episodes. At 26 episodes it's a bit of a slog, but worth it if you're into the history.