Some opensource software l used for video editing include Blender 2.8.2 and Openshot. Blender is available for Linux and Windows. Openshot only runs natively on Linux. Another alternative is DaVinci Resolve.
Below is the settings l used in Blender 2.8.2 – the latest release at the time of this post.
In this case l was exporting a iMovie iPad created 4K MOV file to streamable MP4 H.264 file format for playback on my TV. Dont forget the settings for the audio section. This settings also work for video targetting Youtube [UHD/HD etc] and Instagram [set max video width to 1080 is preferred].
Set the rendering to Cycles [not eevee] , GPU, GPU compute – this helps if you have a good graphics card. In my case, my main video editing/programming workstation has an Nvidia GTX1080 w/8Gb. CPU as below and 32Gb RAM.