How can I edit out the flicker from a projector from existing video footage?
tomh's advice to double stack the video layer, reduce opacity by 50% and advance a frame is a great starting point and certainly works well on fluorescent light flicker.

I've just had the same problem with a single chip DLP projector image in shot with the banding looping over about 5 frames. Working in Premiere Pro, I layered the video 3 times, cropped each layer to the projection screen area, reduced each layer to 25% opacity and advanced each layer 1 frame on from the last. I also reduced the brightness on the base layer by 100% (referring to Lumetri Scopes and using my eye to avoid blowing out the slide image). It's a very satisfactory result.

Caveat: If anything crosses the projected image is will look like it has a strobe effect and any animations, video or transitions will have this also, however for a set of static slides you should be fine.

I got a bit carried away and made an example video...

Hope this helps you or anyone else using a search engine to love their quirky issues like i did to find the original post.