hi ,
Please check that your PC or network are NOT using Virtual Private Network (VPN), by accident or design.
The Fortnite Game client detects VPN and rather than banning people as before just removes networking files to block this Fortnite/UEFN.
Please also check that your Anti Virus software is not removing parts of UEFN/Fornite files as they regard them as infected.
Excluding UEFN and Fortnite from Windows Defender for Windows 11
In the Exclusion section try and add the Fortnite and UEFN binary directories to be stopped from scanning as in past this has caused similar problem.
After adding anything to an Excluded list you must click the three dots next to launch and select Verify to put back the original files