this is what comes up in the terminal
Last login: Fri Sep 1 19:51:13 on ttys000
/Applications/Slicer.app/Contents/Extensions-31938/SlicerIGT/lib/Slicer-5.4/qt-loadable-modules/libqSlicerFiducialRegistrationWizardModule.dylib ; exit;
(base) jaymegoodrum@Jaymes-MacBook-Air ~ % /Applications/Slicer.app/Contents/Extensions-31938/SlicerIGT/lib/Slicer-5.4/qt-loadable-modules/libqSlicerFiducialRegistrationWizardModule.dylib ; exit;
zsh: exec format error: /Applications/Sl
exec format error: /Applications/Slicer.app/Contents/Extensions-31938/SlicerIGT/lib/Slicer-5.4/qt-loadable-modules/libqSlicerFiducialRegistrationWizardModule.dylib
Maybe the extension package was corrupted while it was zipped, downloaded, or unzipped? Could you check if the files that you have on your computer are the same as those that you can download from the Extensions Catalog?
There seems to be something wrong with the extension packages on macOS on Slicer-5.4. While we are working on a fix you can use Slicer-5.2.
@Sam_Horvath Are you aware of this issue? Is this something that you can have a look at or we need to wait for @jcfr? Do you know when he is going to be available?
Thanks for pointing this out, I will be looking into this today and follow up.
The root cause has been identified and fixed 
Valid stable extensions are expected to be uploaded in the next 12 hours 
For more details, see New extensions can not work on Slicer 5.4.0 on MacOS - #4 by jcfr