Board Thread:Technical Updates/@comment-24006128-20200709172956/@comment-37336800-20200709213747

Second half of the sentence MisterWoodhouse wrote: After lots of great work by our engineers, JS Review has been unblocked for UCP and we'll be able to start enabling custom JavaScript on UCP wikis soon!
 * (emphasis mine)

Meaning that it's not available at this time but will be soon