VLC Media Player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, mp3, ogg, ...) as well as DVDs, VCDs, and various streaming protocols.

If you do not want to install heavy video editing software, you can merge videos using the Photos app or VLC media player. The Photos app is an in-built image viewer for Windows 11/10.