Maybe not quite on the spot, but a Storage Share (hosted nextcloud) from Hetzner might be an option.
Bonus features and info: You can also share other files, location, calendars, contacts etc. They have a compliant data protection agreement, and are fully GDPR compliant.
Hetzner Storage Share: https://www.hetzner.com/storage/storage-share
Good question, but no ๐
OS2 is a organization which coordinate software development for the participating municipalities and companies which sign up for delivering FOSS. I think OS2 stand for Open Source Software, but not sure.
More about OS2 here: https://www.os2.eu/in-english