Client is coming from WP and is used to Elementor (https://elementor.com/). Can create own rows, columns, etc. in content. Is there a visual editor for Craft 3? Client hasn't specifically requested but think they'd like more than just rich text.
If you are looking for "drag and drop" I would use matrix blocks. You can define text block, image block, video block, etc that would be available in Elementor.
Maybe you don't get as much out of the box as a plugin, but you are able to define exactly what is available to the client.
Happy coding :)
Yes, you will have to define the elements that the client will manage for a page. If you watch the video in craftcms.com landing page you can see how that would look like.
The elements on the left are the fields that you would define (from a field type) and then you would add them to a Craft section.
For the rich text you have Redactor field type, which you can add to your Craft instance when installing the Redactor plugin in the plugin store.