1. First, let's check your current DNS settings:

cat /etc/resolv.conf

2.Try to ping GitHub:

ping github.com

If this doesn't resolve to a proper IP address, we need to fix your DNS.

3.Try using Google's public DNS servers temporarily:

sudo nano /etc/resolv.conf

Add these lines at the top:

nameserver 8.8.8.8
   nameserver 8.8.4.4

4.Save the file and try to ping GitHub again:

ping github.com

5.If this works, you may want to make the DNS change permanent. On Ubuntu, you can do this by editing the NetworkManager configuration:

sudo nano /etc/NetworkManager/NetworkManager.conf

Add these lines under the [main] section:

dns=default
   systemd-resolved=false

6.Then, edit your connection settings:

sudo nano /etc/NetworkManager/system-connections/your_connection_name

Under the [ipv4] section, add:

dns=8.8.8.8,8.8.4.4

7.Restart NetworkManager:

sudo systemctl restart NetworkManager

8.If you're still having issues, you might want to check if systemd-resolved is interfering:

sudo systemctl status systemd-resolved

If it's active, you may need to disable it:

sudo systemctl stop systemd-resolved
   sudo systemctl disable systemd-resolved

After making these changes, try your SSH connection to GitHub again. If you're still having issues, let me know and we can investigate further.