I have successfully made a multi-column sidebar layout! FlowTiwi - a Multi-column draggable resizable sidebar (beta release) - #3 by linonetwo
It is using GitHub - react-grid-layout/react-grid-layout: A draggable and resizable grid layout with responsive breakpoints, for React. and thus didn’t take much of my time to implement it. (more time is spend on renderTiddler gets empty result... · Discussion #6645 · Jermolene/TiddlyWiki5 · GitHub )