I have also tried installing the woopress core plugin 1.1.0 via ftp in my dev environment as part of my Woopress 6.0 update testing.
It fails on trying to create the directory; woopress-core/inc/img. however I could see that the img directory was created on the server (it is empty)
I have downloaded the file again, extracted and tried uploading again ,same result.
I have also tried by same method as previous posters via plugins menu on dashboard and get the same error message as they have reported.
I then tried deactivating the plugin and then updating it (got the same ftp error) and then activating. This time it is now showing as 1.1.0 and active! The img directory is created and still empty.
Anyway, thought I would pass this on in case it helps others. Will carry on testing …..
PS My environment shows as meeting all system requirements in the new theme dashboard.
Cheers.