Lightroom mobile shows a "raw" or "dng" tag on top of the image thumbnail. You can further sort images by name, date and other fields. You may also choose to import only raw or jpeg images. See https://helpx.adobe.com/in/mobile-apps/help/lightroom-mobile-faq.html
I normally use the search icon after selecting an album. Typing .cr2 into the search box and hitting return brings up all my raw file results.
Thats not working, this also lists smart previews.
Of course it does, smart previews are "proxies" of the original images. If you want to exclude smart previews from your search, you can additionally use the Sync Status on the Filter Bar, selecting "Synced and Backed Up" will show only files stored in the cloud as originals, whereas selecting "Synced from Lightroom Classic" would only show the smart preview proxies.
Select the album, then type "exension" (without the quotes) into the search box.....that will list all the different file-types in the selected album. Tap on one to reduce the selection to just files with that extension (or just type the extension directly into the search box as 99jon suggests).
Thank you all for the answers. I found out that if I type only "e" in the search field I get all the possible extensions that I can filter. For some reasons on my smartphone "extension" and "jpg" don't work.
Try adding a colon