Hi there 
I have a quick question: 

I was successful to install and use a new font in LMTX (New Computer Modern). All good except that I’d like to use the »Book« variant instead of the »Regular« variant (NewCM10-Book.otf vs NewCM10-Regular.otf). Trying many ways but the right one. 

please advise, 
can I define something similar like \bf for bold — maybe \bk for book?

… all I get is

hp@mbp16 ~ % pdffonts page1.pdf 
name                                 type              encoding         emb sub uni object ID
------------------------------------ ----------------- ---------------- --- --- --- ---------
CRBMBE+NewCM10-Regular               CID Type 0C       Identity-H       yes yes yes      1  0

my definitions are:

\definefontfamily [newCM] [rm] [newcomputermodern10]
\definefontfamily [newCM] [ss] [newcomputermodernsans10]
\definefontfamily [newCM] [tt] [newcomputermodernmono10] [scale=0.85, features=none]
\definefontfamily [newCM] [mm] [newcomputermodernmath]
\setupbodyfont[newCM, rm, 10pt]

Many thanks
Heinrich