I recently read about GitLab’s solution ti this, and it was quite intriguing. They have a 3000 page employee handbook, with everything basically since the beginning. They intentionally subscribe to a Slack tier that does not allow them to keep messages for long, which forces them to put things in the handbook. And then I assume the first answer to any question is “look in the handbook”.
So basically, use some documentation that everyone can use, and make it painful not to use it.