Hey atporsch, thanks for reaching out and sorry to hear about the issue you're having.
I believe you are referring to Assasin's Creed Valhalla rather, however correct me if I'm wrong. If it is the case indeed, please note that this is a dedicated forum section for Assassin's Creed Odyssey queries and to access Valhalla forums, you can click here.
As far as the issues goes, it would be great for us to know which particular cairn are you having difficulties with and as far as the screenshot goes, you can just simply upload it to any image sharing website and then send the link over to us so that we could take a look.
Should you have any questions, let us know!