Sorry I don't get it. Do all Eventide plugins not work at all with Catalina? Or only some plugins? Or only certain features of some plugins? Please, could you clarify this? Information here has been pretty vague.
At this time we're not aware of any problems with the plugins themselves, but we've found some issues when running our installers on Catalina. In particular, access to the Documents directory has been restricted, and that's where we've historically kept presets and documentation. If you've upgraded to Catalina and already have Eventide plugins installed, they likely still work. Running a fresh installation on Catalina may or may not work for you with the current installer versions, and we won't be able to provide support to Catalina users until we've officially released Catalina-compatible installers.
In short, if you're not on Catalina yet, we advise sticking with your current OS for a bit longer. If you're already on Catalina and want to give it a shot, it's quite possible that you'll be able to get it working, but you do so at your own risk. I hope that helps!