I would like to upload files from my inHouse application and store them in a wix collection, is that possible?
I would call wix from my application, send a file to a given collection/folder, and then use wix media to look at the files (.jpg,img,…)
Yes this is possible. You can create an endpoint in your Wix site that you can then call from your external application. This is a good place to start reading about how to do that https://support.wix.com/en/article/velo-exposing-a-site-api-with-http-functions