I've found Lightweight Architecture Decision Records (as markdown docs in a repo with the code, or wherever makes sense) to explain the current landscape, options, decision, and foreseeable consequences. Keeping it really light makes it tolerable for people who don't like to write docs, though does need the team to insist on the doc for anything non trivial.

I also like using the Draw.io vscode extension to draw diagrams without having to export into a separate file or copy into the repo.