VoiceAttack itself has no GUI option to make its window translucent, nor does it make itself translucent by default.
Unless you're specifically launching it with the "-opacity" command line argument, or have configured it to execute a command that explicitly changes the window opacity (E.G. via the "Perform a Window Function" action or an inline function), that would be something to do with a third-party profile and/or plugin you have installed.
Should this have something to do with the third-party HCS Voice Packs product(s) you're using, specifically, they can be contacted via
their forum, or
their Discord.