In Nextcloud, on the blue top-bar, click on your profile picture. A dropdown menu opens, click on "Administration settings".
In the left sidebar, click on "Electronic signatures".
Open a new browser tab and head over to eID Easy sign-up page and authenticate yourself either with one of the native methods or by setting an email and password: https://id.eideasy.com
Confirm your email address as required.
Fill in the Website landing page address (this is the public URL of your Nextcloud instance) and other required fields.