From mystery to solution, how properly decompress a .z

[MakerNeb]

Hello, i m posting here 'cause i'm think is the good place.
I follow numbers of sources and tutorials to face a mildly infuriating dead end.

In the way to explore the 3d models from 3DS Yoshi's new Island, i have extract the romfs by using citra (from a decrypted rom).
But in there, a lot of model information come like this : "name.bch.z"
After some research, i found that be decompress using quickms.

i use the decompress script comming with quickbms but the .bch result is declare unsupported by ohana or spica.

maybe the decompression is uncomplete but i can't find a proper source or scripting about the specific case of Yoshi new island.

so i m calling help on vgr community

Thanks