@treynterrio so you have two option.
codesign/notarize the vst-3 file.
Send it unsigned. Make sure your user/tester has all applications that access the plugin folder closed. Download and migrate the VST3/AU file to the plugins folder. Open the DAW (Cubase in this case). Apple will flag it as malware. Open the system settings, privacy and security, and there you can select allow application.
Both of these options are really annoying but can't be avoided, unless they test the plugin or build it from HISE on their end.