Ecloud browser calendar desktop notifications don't work

I am evaluating ecloud.global as my one and only cloud provider. However, it seems like the browser Calendar app does not properly send desktop notifications.

If I understand correctly, this is probably the same issue I have observed in all other Nextcloud providers:

I have been willing to ditch Google Calendar for years now, but this problem made me miss some important meetings. Maybe I’m a weird guy but proper notifications is critical functionality for a Calendar software. Do you folks know how to solve this problem?