Following the discussion on that thread TextBlock Line Spacing - #13 by gabrielheming
I have found a bug that gives different results when the font size is processed as priority (!important) in the DOM.
The solution is replacing the line below
text.style.font = font;
With this:
text.setAttribute('style', `font: ${font} !important`);
Any other attempt that I tried hadn’t worked. Though, it will be isolated inside that method with now external break changes.