the tutorial aren’t clearly
https://www.high-logic.com/font-editor/fontcreator/tutorials/how-to-make-a-variable-font
why my font aren’t interpolate? while the axis has updated
You still need to merge the two fonts as explained in the tutorial:
Within the Font Properties panel, select the Masters tab. Click the [+] toolbar icon and choose the Bold font.
You need to do this while the Regular font is active.