Saw a couple of them in this weekends Bundesliga. Collapse down to the front like a giant flag would but don’t fold like a flag.
I know I’m probably making an idiot of myself but that’s not the first time. Are they some form of hologram?

Perhaps it's a superimposed image that gives the appearance that it is actually in the stadium but is merely a camera trick? I have not seen this so it's just a guess, I could be wrong, I usually am.

Remember the cardboard cutouts when Covid stopped people attending.

Thanks for replies but I think I’ve worked it out. It is hung from the front of the stand roof and lowered vertically. Not like the flags that are passed down over the fans heads.

It's called a tifo. The design is printed on transparent netting and as you say, hung vertically from the top of the stand (or sometimes by the fans).

Explained: What is a tifo banner? https://share.google/oLywq7I8KUfCZS9BR

The Wolves fans did it very well in respect for Jota this season

https://www.facebook.com/reel/1703399113691847