How to merge multiple videos using VLC:
Use this free online CapCut website without any watermark or an actual DOS command:
"C:\Program Files (x86)\VideoLAN\VLC\vlc.exe" 1.mp4 2.mp4 3.mp4 --sout "#gather:std{access=file,dst=final.mp4}" --sout-keep
Source = YouTube
"C:\Program Files (x86)\VideoLAN\VLC\vlc.exe" 1.mp4 2.mp4 3.mp4 --sout "#gather:std{access=file,dst=final.mp4}" --sout-keep