Because there's no tree-like hierarchy, it's quite difficult surfacing information unless you know exactly what you're looking for. And while some people will know what they want, I find it beneficial to make everything as visible as possible, since more eyes means it's less likely for documentation to go stale.
At work, we've currently trialled a multi doc site using MKDocs, with different topics, published into GCS buckets, and sourced from a git repo. mdbook and gitbook offer similar strategies.
Discourse is similar to stackoverflow, and has the advantage of people being able to ask questions, but it's not the best medium for documentation.
I think something light like mdbook might be the right choice to start with, it wouldn't tie you into any particular solution, as your documentation would live in markdown, but would be consumed from a nicer, more polished UI.
This, of course, assumes you're all familiar and comfortable with markdown, but I think the best solution is to try different tools, so the more portable your actual docs are, the better.
Notion is also a very good candidate, and IMO, a better choice than Confluence, but similarly, discoverability isn't great