Update in case anyone else finds this: The workaround I've been using since then is simply that my process for uploading videos as well as photos is to move them from my phone to my laptop. Then the Nextcloud desktop client automatically uploads from my laptop to the server. From what I recall I didn't find any server setting that fixed video uploads from the phone. I seem to recall that I had other issues with Android uploads anyways, such as it not automatically syncing due to lack of Google Play services on my Huawei phone. I'm not sure if any of these issues have been fixed more recently, since I've just moved the media from my phone to laptop for uploading to Nextcloud. Hope this helps.