There are driver blobs for the underlying device which they can't do much about, and then there are the last vestiges of Lipstick (the Sailfish OS UI), which are not released under an open source license. That's hardly "the whole OS", since everything else is a plain linux distribution.
Basically all the middleware in Sailfish OS was always open source and many of the apps as well. They have been also IIRC finally open sourcing the primary apps as there are no longer pesky external investors forcikg them to keep things closed for weird reasons.
There are driver blobs for the underlying device which they can't do much about, and then there are the last vestiges of Lipstick (the Sailfish OS UI), which are not released under an open source license. That's hardly "the whole OS", since everything else is a plain linux distribution.
Basically all the middleware in Sailfish OS was always open source and many of the apps as well. They have been also IIRC finally open sourcing the primary apps as there are no longer pesky external investors forcikg them to keep things closed for weird reasons.