Your launcher is out of date and cannot connect to the server until it is replaced. Your game files stay where they are - only the launcher changes.
The newest version, straight from our update server
Packed as .xz - open it with the free 7-Zip or another archive tool, then put L2Ertheia Launcher.exe into your Lineage 2 game folder in place of the old one.
Get the new launcher above. It comes packed as an .xz archive, so you need an archive tool such as 7-Zip or WinRAR to open it.
Unpack the archive with 7-Zip or another archive tool and move L2Ertheia Launcher.exe into your Lineage 2 game folder, overwriting the old launcher there. It has to sit in the game folder, or it cannot update the game files.
Run the new launcher from the game folder and let it check the game files - depending on your PC that can take a few minutes. Then log in as usual. Starting L2.exe directly will not connect to the server.
If the update gives you trouble, the answer is usually here
Something stopped the launcher from overwriting itself. Most often an antivirus holds or quarantines the new file, the game sits in a protected folder such as Program Files, or a second launcher window was still open. Replacing the file by hand fixes it; to avoid it next time, add the game folder to your antivirus exceptions or move the game out of Program Files.
Windows does not always open .xz archives on its own - you need an archive tool. The free 7-Zip works: right-click the downloaded file and choose 7-Zip → Extract Here. WinRAR and most other archive tools open it too.
The launcher patches the game files, which some antivirus programs treat as suspicious. It is a false positive - add the game folder to the exceptions and run the launcher again. If Windows shows "Windows protected your PC", click More info and then Run anyway.
You are most likely still starting the old file. Check that the new launcher replaced the old one in the folder you start it from, and that your desktop shortcut points to that folder. If it still happens, download the file again - the link above always leads to the newest version.
Open a support ticket in your account panel and the team will get back to you - attach a screenshot or the launcher log if you have one. For a quick question, our Discord is open all day.