I had this problem on an older MacBook Pro where the visuals for all of my FabFilter VST3 plugins won’t work. They are clearly recognizing the audio, as in the case of Pro-L2, where it shows a line for the LUFS level, but no audio visuals scroll. Similarly, nothing shows up in the spectrum analyzer of Pro-Q3.
I just got a new (to me) MBP, and the same thing is happening. I’d be fine with sticking with the VST2.x’s, but they don’t work very well, namely that I can’t save & reload a preset. Whatever I do, it just loads the default settings anytime I load a preset in any FF plugin.
Not all VSTs support Audacity. Most commercial plug-in developers have a list of officially supported hosts but a quick-search didn’t find anything on the FabFilter website.
I have FabFilter Pro-R and Pro-Q 3. When I open either one to apply to a WAV file, Audacity crashes about half the time. It happens so often that I now routinely save the file just before opening a FabFilter plug-in. Yes, it’s annoying. But it’s something I’m willing to tolerate on a free DAW.