Incompatibility between Beamer and STIX 2 Font

With Modern Fonts

If you’re running LuaLaTeX, you can use unicode-math. This supports Unicode and all TrueType and OpenType fonts, and wipes out a lot of the technical debt LaTeX owes to the 1980s. For example, fonts needing to pack all their math symbols into a limited number of 256-character math alphabets and doing that in different ways. I personally recommend that you use the modern tools whenever you can, and the legacy fonts whenever you have to.

\documentclass{beamer} \usepackage{unicode-math} \defaultfontfeatures{Scale=MatchLowercase} \setmainfont[Scale=1.0]{STIX Two Text} \setmathfont{STIX Two Math} \begin{document} \begin{frame} \[ Re \approx 10^8 \] \end{frame} \end{document} 

I also removed some package options that you no longer need. (LaTeX 3 already makes UTF-8 the default input encoding, and the class can detect which engine it’s running on.)

You can change the text font to whatever you please, or define a separate \setsansfont. See the documentation of fontspec if you want the details.

It’s also possible to use a font of your choice for variable names in math mode, along with the symbols from your math font, with the range= option of \setmathfont. See the documentation of unicode-math for the details.

With Legacy 8-Bit Fonts

The problem here was that beamer tries to substitute some of the fonts in the document. If you run pdffonts on the PDF file you get, you’ll see that it’s trying to use LMSans (Latin Modern Sans) instead of STIX Two. The class detects certain font packages, as well as unicode-math, and changes its behavior to be compatible with them. However, stix2 is not one of those packages (as of 2020).

You therefore need to turn these substitutions off with professionalfonts:

\documentclass[professionalfonts]{beamer} \usefonttheme{professionalfonts} \usepackage[T1]{fontenc} \usepackage{stix2} \begin{document} \begin{frame} \[ Re \approx 10^8 \] \end{frame} \end{document} 

You can load whatever other fonts you want after stix2. If you want to stick to sans-serif fonts as the default, for example, you can \renewcommand*\familydefault{\sfdefault} or load a font package with a [sfdefault] option.