Steps to reproduce

Since creating a new event does not work in version 2.0.4 (Invalid date Invalid date). I'll give an example in the Tasks app. I create a new task list, share this task list with other users, add new tasks to this task list. These tasks appear in the calendar application, but no user is notified of a new event or new task. Notifications are enabled in the settings. For example, notifications from the Talk app work and come normally! I am using system cron to call cron.php

Expected behaviour

Users should be notified of a new event or task.

Actual behaviour

Users do not receive notifications.

Calendar app

Calendar app version: (see apps admin page, e.g. 2.0.1)
2.0.4

CalDAV-clients used: (Thunderbird Lightning, DAVx5, Evolution, macOS Calendar, etc)
Not used

Client configuration

Browser: (e.g. Firefox 48)
Firefox 81.0.2, Chrome 86.0.4240.75, Opera

Operating system: (e.g. Arch Linux)
Windows 10

Server configuration

Operating system: (e.g. Debian 8)
Linux Ubuntu 18.04

Web server: (e.g. Apache, Nginx,...)
Apache + Nginx Proxy

Database: (e.g. MariaDB, SQLite or PostgreSQL)
MariaDB

PHP version: (e.g. 7.0.3)
7.3

Nextcloud Version: (see admin page, e.g. 17.0.2)
19.0.4

Updated from an older installed version or fresh install:
19.0.3 fresh install and 19.0.4 updated from 19.0.3

List of activated apps:
Accessibility, Activity, Audio Player, Audio Player - ID3 Editor (add-on), Brute-force settings, Calendar, Collaborative tags, Comments, Contacts, Contacts Interaction, Deleted files, Federation, File sharing, First run wizard, Group folders, Log Reader, Monitoring, Nextcloud announcements, Notes, Notifications, ONLYOFFICE, Password policy, PDF viewer, Photos, Privacy, Recommendations, Right click, Share by mail, Support, Talk, Tasks, Text, Theming, Update notification, Usage survey, Versions, Video player