Possible scenarios:
[root@######:~] esxcli system ssh server config set -k PubkeyAcceptedAlgorithms -v ssh-ed25519
Ignored key [pubkeyacceptedalgorithms] as it doesn't belong to the list of configurable properties
vSphere ESXi all versions
ed25519 is currently not supported to be used by ESXi.
The list of supported key algorithms can be obtained with the command "esxcli system ssh server config list"
The default list of key algorithms is this asper value of "hostkeyalgorithms":
ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,rsa-sha2-256,rsa-sha2-512
Use only the supported key algorithms as per:
ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,rsa-sha2-256,rsa-sha2-512
Any further add-ons are not really supported as they are either not made available or not FIPS compliant.
Important!
Note that by limiting or changing the key algorithms to be used by SSH server on ESXi will cause SSH clients to not be able to access the SSH server on ESXi.
For instance, since Putty uses specific algorithms for the connection it will fail with the error "Couldn't agree a host key algorithm (available: )" if none of it's required algorithms is allowed by ESXi.