I do know the pain. Maybe if you move the documentation out of a third party application it could help.
Move it to the codebase, Like in a folder containing markdown or rest files. Adjust your definition of done. Changed behavior? The change only gets merged if the corresponding doc was updated or created. You could generate static HTML files from there or even import it in a CMS/Wiki/Anything.
Unfortunately there is no silver bullet to this. Just plain discipline.
Confluence is the third-party! :D
I find that the README.md of every project is one the most important things. We usually only have setup there, but you always know where it is. Maybe having a wiki in each project repo... not that you could put everything there, but what was project related, everything else would just add info and link to there.
Problem with repo for wiki is that not all involved will go through the effort of writing markdown and using a VCS. Search and organisation would still be a problem, unless you added something on top of it that added at least search. Biggest point here for me is version control and the ability to do PR's for wiki, that would be a major plus!
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