Hi. Great to read about your experiences. Thanks for sharing.
I tested Taiga, Leantime, Wekan and many more open source project management tools.
We're a small non profit organisation from Germany. Our people work pro bono (without payment) in their free time.
Although Taiga, Leantime and Wekan seem to have the feature to notify people via email when their task due date is reached, that didn't work when we tested it. It's a feature we need since most of our people don't regularly open their project management tool.
Vikunja was the only solution that had that feature.
I also tested: Gitlab, Github, Kanboard, NextCloud Deck, FOCALBOARD, Mattermost Playbooks, Odoo, Planka and Trello.
Do you know a free project management tool that has those mentioned email notifications?