I'm using Plone 6-beta with Volto as front-end and I have noticed that several useful features of the WYSIWYG editor have not been implemented, such as local search for images and internal links.
@u.calligaro For block pages, images can be inserted using the Image block. Think of the whole blocks as a whole image editor.
For the richtext editor in other places (sidebars, schema fields, etc), there's limited support for images.
I don't know what you mean about internal links. When you select some text, using the Link button you can also click the Browse button to lookup targets from the site objects, using the ObjectBrowser component.
In "standard" layout, when you click on the link icon in the editor, it's open a modal with the options to insert the link as a link to a page of the website, to upload a file, to insert an external link, to insert an email-to link or link an anchor.