https://grapesjs.com is an open source option, but will require some investment to get it working for your situation.
There is also Wordpress, Squarespace, and Webflow. Webflow has a CMS section. Netlify has some options here too, CMS system with a web UI.
I personally use Hugo (https://gohugo.io) and Webflow. Planning to use something with grapes+hugo to replace webflow.
Has a free edition and a paid edition with more features. WYSIWYG features like a word processor.
Don't forget that Word and LibreOffice Write can export HTML files.
I'm not however happy about the workflow (non technical users found it too difficult). So I wonder what workflow you had in mind...