The search prototype will allow people to search for multiple filetypes at once (see https://phabricator.wikimedia.org/T212262)

It is currently possible to search for files of only 1 filetype (e.g. filetype:bitmap) or the inverse (-filetype:bitmap).
These filters are AND-ed, so a query like so: filetype:bitmap filetype:video, will find results that are both a bitmap & video. I.e. nothing.

It is somewhat possible to search for multiple filetypes already by negating all other filetypes. E.g.: -filetype:unknown -filetype:drawing -filetype:audio -filetype:multimedia -filetype:office -filetype:text -filetype:executable -filetype:archive -filetype:3d to find results that are either a bitmap or a video.
This is quite cumbersome though, and requires knowledge of all the (other) supported filetypes. It's quite possibly also not the most optimized solution to find the results needed, and how to rank them...

We should probably add proper support for searching for multiple filetypes at once, probably in a way similar to a few other filters (with a separator char), like: filetype:bitmap|video