Description

Optical sizes can (since #3315) be selected by manually adding the size to the font name. LaTeX automatically selects the correct optical size (if available), or uses scaling as a fallback option, while Typst appears to only scale fonts.

Minimal working example (Typst):

#set page(
  width: auto,
  height: auto,
  margin: 5mm,
)
#set text(font: "Latin Modern Roman")

#let demo(size) = {
  box(height: 2cm)[
    #scale(2cm / size * 100%, reflow: true)[
      #text(size)[Aa]
    ]
  ]
}

#demo(8pt) #demo(10pt) #demo(20pt)

Output (unwanted, all pairs look identical):

Minimal working example (LaTeX):

\documentclass[border=5mm]{standalone}

\usepackage{adjustbox}

\begin{document}

\def\demo#1{%
  \strut\adjustbox{height=2cm}{%
    \fontsize{#1}{0}\selectfont Aa%
  }%
}

\demo{8} \demo{10} \demo{20}

\end{document}

Output (note differences in stroke contrast between pairs):

Use Case

I'm the author of typst-metalogo, and the 'A' in the LaTeX logo has different metrics and stroke width when compiled with Typst instead of LaTeX. This results in the logos looking 'unbalanced' in Typst due to the differences in stroke width between the regular and scaled glyphs.