When launching it gives an error

[KIttenPixel]

when I launch BOTW from BCML it gives the error

You must perform a system update to play The Legend Of Zelda: BOTW

Returnng to Wii U Menu

On normal cemu this does not occur

[GingerAvalanche]

You don't need to launch Cemu with BCML, the button is there for convenience. Once the mods are installed, you can just open Cemu regularly.

[ArchLeaders]

This likely means you have two Cemu instances, one with the botw update installed (this would be the Cemu you run normally) and one without the botw update (this would be the one BCML is pointing to), change the BCML settings to point to the first instance that you're running manually (I.e. the one with the botw update installed).