IIRC Confluence defines its own dialect of Markdown as well, but I don't think the issue is the tech so much as enforcing some minimum discipline in encoding knowledge formally in a central, organized repository. That takes building a culture which in turn takes investment from management to acquire as far as I can tell.

Until then, I'd rather have things decentralized in their appropriate Github/Gitlab repository with issues and a wiki. At least this way you have all functional blocks of knowledge absolutely in one place since you can get code history, closed issues, and the wiki history in one place. I'd even go a step further and have design/UI as a directory in the repo.