Cannot save files to Icedrive on a Chromebook

Using web based Office for Word, PPT etc… on my Chromebook.
I can save files to Onedrive and Google Drive, but cannot save to Icedrive - the option doesn’t appear.

I have the Icedrive app installed, and I can access my Icedrive files when using the ‘Files’ app. However Icedrive doesn’t appear when saving from

Is this possible?

Can’t you just upload your files to the Icedrive web site?
Why use an app?