That's why you have someone whose job is to make that Notion/Confluence/Dokku who is part designer, part technical writer. They're sometimes called company historians.

It is the only solution I've ever seen for the "documentation always gets cut" problem with SWE. Someone's whole work stream is thorough documentation and knowing everything. How features work, what customers requested them, what technical trade-offs were made and why.

I miss having one of these people every day at $dayjob. She would make reports for questions that's needed a thorough response. I asked what I thought was an innocent question about what a small kafka cluster was used for and I got back a long-ass document that outlined the whole saga, the complaints the customer had, the VP discussions, the MRs that introduced it, other things people proposed and why they were shot down, meeting notes, screenshots of the discussion on Slack. Like hot damn.