The black and white Noto emoji have not been updated in years sadly, but you can still pretend it before Noto Color Emoji. Alternatively prefer Symbola, which should be more up to date.
Couldn't you just strip the tables for the color map and the additional glyphs for the other color layers? Or does Noto use bitmaps or SVGs for the colored glyphs?
It's a scalable bitmap glyph as far as my understanding goes. "It's scalable even though it's a bitmap font." is what I remember reading last year, but I cannot find it for you, sorry.
From looking at the Github repository, it seems like the source images are SVG and the font might use either SVG or bitmaps, but not COLR/CPAL which would degrade nicely to black and white.