When running a Java 21 application that uses fonts on trixie (13), I get
the message:
java.lang.UnsatisfiedLinkError:
/usr/lib/jvm/java-21-openjdk-amd64/lib/libfontmanager.so:
libharfbuzz.so.0: cannot open shared object file: No such file or directory

Manually installing libharfbuzz-bin solves the issue for me.

I attach the Dockerfile of the container image that I use to run the
application as an example. (I.E. with the manual fix for my situation)

Greetings.. Mark

this is packaged this way by intent. you don't need a dependency on
libharfbuzz-bin, but on libharfbuzz0b.

openjdk-21-jre-headless recommends libharfbuzz0b, and openjdk-21-jre
depends on it.  So either install the recommendations, or install the
openjdk-21-jre package.