It is the confetti of the general team color held out by the launcher behind the rostrum.

There is a small paper tube at the bottom, which contains a small amount of gunpowder, and then it will spray out colored scraps of paper. Often used in large-scale wedding activities, it should be sold in gift shops, wedding companies, flower shops and so on. If you can't find it, there must be such a thing on Taobao, which is not too expensive and has no technical content.