If using Sforzando 1.982~beta3 as VST3, under Ardour 8.12.0 Linux, the file load dialogues in the Sforzando plugin don’t show up when clicking on load or import. They show if using Sforzando standalone or as VST3 through Carla.
(I’d be willing to bet on some kind of shared library madness.)
If I had to guess. They fork a separate process to show the file selector UI (which is really bad practice for various reasons)
Maybe the workaround (or a variant thereof) presented here can help:
By Jove, Holmes, you are right!
/usr/bin/zenity: symbol lookup error: /lib/x86_64-linux-gnu/libcairo-script-interpreter.so.2: undefined symbol: cairo_set_hairline
However the workaround described does not work. Maybe they try invoking zenity directly as /usr/bin/zenity`?