Independent font size selection was added in v0.30
So, this is a place where Deepdwn is not great, but it was added to at least make custom font selection possible.
The font name used in this case is likely just ‘Neuton’ (it was for me after installing the font from Google Fonts). I don’t believe capitalization matters.
A future update should make a proper font list available, or a better search, but I don’t know when that will be.