raised Net::SSH::Exception (rescued RuntimeError) with msg "could not settle on host_key algorithm with ssh-ed25519

[Atroskelis]

raised Net::SSH::Exception (rescued RuntimeError) with msg "could not settle on host_key algorithm with ssh-ed25519

[marmack95]

Have you check that this ssh algorithm is enable on 2 devices ?

[Atroskelis]

Have you check that this ssh algorithm is enable on 2 devices ?

I don't understand. The specific key is the only one offered by newer fortigates

[marmack95]

Your server seems not support ed25519 algorithm (or it's not enabled).
You probably obtain the same error when you try to connect manually to your device from this server (ssh -vvv mydevice).
This article can help you: https://www.endpointdev.com/blog/2023/04/ssh-host-key/