Hi Max,
I just installed the plugin and found the same problem. It’s on WP 5.0.3. I have deactivated some blocks, but they are available when editing or creating posts.
This is the error from the console:
Uncaught (in promise) TypeError: deactivatedBlocks.forEach is not a function
at deactivator.build.js?ver=c90e878:6
(anonymous) @ deactivator.build.js?ver=c90e878:6
Promise.then (async)
(anonymous) @ deactivator.build.js?ver=c90e878:1
Awesome plugin BTW, thanks!