I’m not a developer myself but I feel like your issue has to do with graphics rather than sound.
Opening the plugin browser window means that lots of stuff needs to be rendered on screen, and this may put a heavier load on the graphics card.
Is it also possible that in general, VCV Rack demands more graphical resources compared to the applications you mentioned.
Be sure to carefully read this, and try the workarounds explained there (example: set a lower framerate) if you haven’t already:
EDIT:
another link - maybe more useful for non-Mac users: