Can't export a file to a cloud (mounted via WebDAV - RaiDrive)

Hello.
Okay, so. I have sucessfully mounted my Nextcloud to Windows via Raidrive (WebDAV). There is a folder that was shared to me, I have all the neccessary permissions for this folder. I can copy files into this folder, I can modify the files there, I can delete the files, I can copy the files from there to my PC.

The only problem I have is that for whatever reason, I can’t export files from different apps directly into the shared folder on this cloud. It says I don’t have permissions to modify the files in there and that I should ask the server administrator.

What I have to do is export the file to my desktop instead (or anywhere) and then move them into the shared folder on the cloud (still via WebDAV).

I really need a fix for this. It is crucial for me to export files directly into the shared folder. Any ideas?

Thanks.
Screenshot with the error message is in czech, however it says what I wrote above. (you don’t have permissions to modify the files, ask the administrator etc.)
image