These are fixed for the next versions except qsv (Quick Sync Video) where it is not implemented because I have not figured out how to map it and not hinder compatibility. Not related to CVBR, but for another example,
Basically, with respect to “map” for QSV, if you setup CVBR and manually add a line to Shotcut’s Other tab: qscale=31; it ends up doing CQP (constant quality) when you check the log. Intel has many rate control methods with compatibility pitfalls making it difficult to map to common methods and access through FFmpeg parameters.