Thanks for your reply.
It is SharePoint Business, but with our SharePoint version the solution in WIN10 "Copy the URL from the browser, the use explorer and “map network drive”, paste the URL" is no longer working.
I can activate the Sync function in SharePoint and find all files on my harddisk and could using it in Affinity (and synced back to SharePoint after saving). But this is only for some files a good idea, but not for an image library of hundrets or thousands of images. Makes no sense to sync all these files and and at some point the local harddisk do not have enough space. And working with colleagues together and all of them sync the same thousands of files to the local harddisk make as well no sense.
Looks like not really working in a useful way.