I've kickstarted a docs centralization initiative at my current work, precisely because of all the issues you described. We have it in version control. There's

I've kickstarted a docs centralization initiative at my current work, precisely because of all the issues you described. We have it in version control. There's a top level repo folder called: documentation and inside there are dedicated subfolders for things like onboarding, testing, domain specific tips/knowledge, etc. A huge advantage of this approach is that the docs are close to the source and in the most logical place for the relevant stakeholders to benefit from them. This has worked quite well!