The MultipleNatFound in the error message is the issue, see this post for instance.
As you seem to have only one router, the problem is most likely your ISP running on IPv6. According to this …
… the port forwarding on the router seems to have been automatically correctly, but this does not help if your ISP is running on IPv6.
However, Roon is currently working on / testing a solution for users with ISP that only have IPv6. If you feel comfortable, you can try this and hopefully get it working: