Source code sent.
In the meantime, can you answer the unanswered question about full screen mode. Every time I open an Adventuron game in full screen, the first thing I do is press Escape and resize the browser window to a comfortable viewing size. I'm sure I've seen a setting somewhere where you can override this default behaviour. If I set itch.io to open full screen, it does the right thing and just maximises the browser window, but as soon as you get past the title screen, Adventuron overrides this and sets it to full screen. That's fine for mobile, but it's definitely NOT fine for desktop, especially when you have a really wide screen.
On the subject of the tiny font on mobile, I initially assumed the default 8x8, but the font was tiny on desktop, so I changed it to 16x16 (as the font was downloaded from http://www.pentacom.jp/pentacom/bitfontmaker2/, where the design grid is 16x16. This looks good on desktop, but it's tiny on mobile. I'm looking at the font's metadata using https://fontdrop.info/. What properties should I be looking for where you said the font may be "lying in its metadata"? This might give me an idea about the correct font width to use and number of columns to use for mobile.
I've just been dabbling with the font size again. In retrospect, the 8x8 font was tiny because of Adventuron's weird scaling. It opens full screen by default and the font is tiny. When you press Escape to get rid of full screen and resize the browser window, the font gets bigger. So the bigger the screen, the smaller the font. Go figure.