I've just noticed that typenames don't get colorized for newly opened documents (this is from editor.h):
<img width="467" alt="Screenshot 2023-09-01 at 20 49 40" src="https://github.com/geany/geany/assets/713965/8255c38b-096b-400b-a035-f772cc504566">
However, when Geany gets restarted and this file is opened from the session list (and not manually), colorization works:
<img width="467" alt="Screenshot 2023-09-01 at 20 50 16" src="https://github.com/geany/geany/assets/713965/1c614c29-bd50-4566-8f01-4c7b8de8f7d9">
I've bisected this to the commit updating Scintilla to version 5 just after the 1.38 release.