game is laggy and high packet loss in Fortnite

Hello eyc0719,
Thank you for reaching out to the Microsoft Community and I'll be glad to assist you today.
The issue you are experiencing while playing Fortnite could be due to various reasons even if your Wi-Fi works fine. First, check if Fortnite servers are having issues - https://status.epicgames.com/

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If there are no known issues, you could try the few methods below to diagnose the network connection and resolve the issue.
1. Run the Network troubleshooter:
a. Search for Network troubleshooter in the search bar on the taskbar, select 'Find and fix problems with Network', and select it.
b. Run the network troubleshooter to find and fix the problem automatically.
c. Once completed, restart your PC and try connecting to your network. If the issue persists,
2. Flush DNS Cache.
a. Open Command Prompt (Administrator) Window.
b. Type or paste the commands below one by one and press Enter after each command:
Type netsh winsock reset and select Enter.
Type netsh int ip reset and select Enter.
Type ipconfig /release and select Enter.
Type ipconfig /renew and select Enter.
Type ipconfig /flushdns and select Enter.
Type exit and click enter to close the command prompt window. Restart your PC and try connecting to your Wi-fi network
3. Uninstall and re-install Wi-Fi Drivers.
a. Open Device Manager.
b. Select the arrow next to Network adapters.
c. Right-click your generic Wireless network driver, select Uninstall device, select the Attempt to remove the driver for this device check box, and then select Uninstall.
d. Once uninstalled, restart your PC.
(Windows will automatically install the drivers for your PC)
e. Try connecting your PC to your wi-fi network and see if it helps.​
4. If the issue persists, perform a Network Reset.
a. Go to Settings and select Network & Internet.
b. Select Advanced network settings.
c. Click Network Reset > Reset now to reinstall your network adapters and set other network components to original settings.
I hope this information helps. If you have any questions, please let me know and I will be happy to help you further.
Best regards,

Gunasekar N

As i said i don't think it's a problem with my internet cause I can play just fine on other games.