After an evening of researching a nice, self-hosted #Kanban board (think Trello) and seeing some of the demos, my despair brought me to the simplest solution.
Use my own #Gitea instance with an empty repo and a bunch of issues managed in the project.
Simple enough, exactly what I needed. And kudos to Gitea devs, they've done some great work on this!
Fosstodon is an English speaking Mastodon instance that is open to anyone who is interested in technology; particularly free & open source software.