Since MediaWiki 1.28, CirrusSearch allowes to search for files with a give Type of file or Mimetype with the keywords filetype: and filemime: (→ T145560).
It is possible to exclude filetypes/filemimes from a search with the exclusion syntax -filetype:audio but it is not possible to combine two filetypes/filemimes alternatively with the 'OR' keyword also provided by CirrusSearch.
Example:
Searching for [[ https://commons.wikimedia.org/w/index.php?search=filemime%3Aimage%2Fpng+OR+filemime%3Aimage%3Atiff&title=Special:Search | filemime:image/png OR filemime:image:tiff ]] should search for both files in png-Format as well as files in tiff-format, instead it return nothing.