Ok, great to see there's no solution lol.
Anyway, I found an alternative. The web interface allows 4Gb upload BUT of course, upload won't finish on Itch. BUT Itch offers Dropbox direct download. BUT Dropbox upload also fails... BUT Dropbox offers Google Drive direct download... And Google Drive upload worked...
So I uploaded to Google Drive, then to Dropxbox, then to Itch... Would be nice if Itch could link to the biggest storage platforms around to make it easier but at least, I got my update online now.
Thank you.