Unable to sync Tasks with any Nextcloud

• /e/ version: 0.15
• Device model(s): Xiaomi Redmi Note 4X, very probably on any device

Summary

It is not possible to sync Tasks app with any Nextcloud service, apart from /e/ cloud. It is not possible to create synchronized lists.

The problem

Steps to reproduce

1. Do not have an /e/ account synched into device.
2. Tasks > Displayed Lists > Synchronized lists > Add list

What is the current behavior?
It is not possible to add a synched list, only local. This is happening since many-many /e/ versions ago.

What is the expected correct behavior?
It should be possible to create synched lists.