1 Answers
Hi Osiris,
The justify button was removed in WordPress 4.7, and it doesn't look like it will be added to the WordPress Block Editor anytime soon, for the reasons outlined in this feature request post:
https://wordpress.org/support/topic/gutenburg-full-justification-feature-request/
Now, you could add some CSS to your theme's stylesheet to force paragraphs to justify. But these days it's considered a bad practice, because it has a negative effect on readability and accessibility.
Hope this helps!