I can also recommend https://www.focalboard.com/
https://github.com/mattermost/focalboard
It seems like it was a successful test product for Mattermost (more power to them).
As far as kanban/task management goes, Gitea/GitLab/GitHub feels like the right place these days (for software companies). Are there any reasons you prefer a standalone tool over putting the PM stuff a bit closer to the code?