We've only just given Nextcloud Collectives a spin - and it actually seems pretty damn good!
It uses my preferred Markdown, is collaborative, simple, accessible, links to Nextcloud Files, seems to maintain links between document when they change path, has all the useful WYSIWYG Markdown tools, including a reasonable implementation of static tables.
What's not to like? (I don't really like the name though, but can't win them all.)
Thought the experience was worth noting as a credible alternative to Notion, Outline, Documize, Appflowy etc, since the conversation and comparison comes up occasionally:
thanks, gonna give this a whirl too