debian12默认不支持旧的RSA KEY登录，需要手动修改配置，添加一个 /etc/ssh/sshd_config.d/enable_rsa_keys.conf 配置文件即可：

cat > /etc/ssh/sshd_config.d/enable_rsa_keys.conf << EOF
HostKeyAlgorithms +ssh-rsa
PubkeyAcceptedKeyTypes +ssh-rsa
EOF

然后重启ssh服务

systemctl restart sshd

reference:
https://u.sb/debian-enable-ssh-rsa-key/