Wiki.js seems like an awesome solution to manage WIKI’s but I don’t see how it can be integrated in a Frontity project as:
It doesn’t seem to provide integration w/ Wordpress
The frontend doesn’t seem to be done w/ React
Anyway, you could develop you own documentation system using WP + React w/ Frontity.
In Frontity there’s an open discussion about migrating the documentation to a system using WP + React + Frontity.