Based on the information you have provided we can see that you have different problems with external connection from your Roon Server.
The first post claims that you have Multiple NAT. In order to cope with that you might need to enable manual port forwarding on all your routers at home and make sure that your ISP does not have NAT. In case your ISP has NAT you’d either need to buy a white static address or ask them to forward the relevant port for you.
In your second post we can see that you have general Time Out error which likely means that you have a problem with port forwarding. Thus, can you please create a manual port forwarding rule for TCP on your router and share a screenshot with us ?
If none of the above works you might stick to VPN solution. Here is an instruction on how can you set it up so you would not need to deal with network setup at home:
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Also, we did not see any Roon ARC records in our database, did you try to connect to the Roon Server from your Mobile Roon ARC app ? Sometimes it works even despite Roon Server says that connection could not be established.
As an addendum to the post above: the Nucleus+ doesn’t have a built-in Tailscale interface in RoonOS like other Nucleus models, so you will need to set up a second device in your network as a Tailscale subnet router in order for the proxy VPN to work. Any MacOS or Windows computer - even an AppleTV or a Raspberry Pi - can function fine in this role.
This is a somewhat arduous process compared to the alternative, which would be to request a dedicated external IPv4 address from your internet service provider directly.