What about the static effect of background people flying out of the background in AE?

There are three composition groups. The first group is the static background you mentioned.

The second group stores the picture material to fly out, and the third group is a particle filter. The specific values in the options are adjusted by yourself. Among the options, there is an option to replace something (don't forget it for a long time). Select this as the second composite group. The principle is simple, that is, replace particles with other composite groups, and all the properties of particle groups are applied to the replaced materials.

In that case, you should understand.