Also, if you wanted something more customized and jerry rigged, push notifications is very easy with ntfy. Its just a webhook so you could theoretically make anything a notification.

Baikal backend, DAVx5 android app and tasks.org android app.

Thats what you want. All open source.

Been using for notifications for a while and its great.

Self-Hoster 🏡

• Fleet: 2–3 devices · 1–4 TB
• Motivation: Independence from Big Tech & subscriptions, Learning & experimenting, Privacy & data ownership
• My MVPs: Actual Budget, Baikal, Memos, Termix, Jellyfin