Source-File for example 4,5 GB, I will export this in 5 files with 1GB for each file --> 4 x 1GB + 1 x 0,5GB.

There is already a feature of cutting into even time slices. The problem with cutting based on size is that we need to translate size into time values in order to divide it. We could estimate by dividing input file total size by the duration in seconds, but because of VBR (unstable bitrate) throughout the video, it will not be accurate. Meaning some files could become 1.1GB, others 0.9GB, etc