I do get the blocks shown when I click the plus sign. However, even when I move the e.g., text block, I cannot change the text in the text block, even when double-clicking. Do you know what is wrong?
When you can drag blocks in but double-clicking a text block does nothing, it’s usually one of these:
1. **The theme is a legacy HTML (non-MJML) theme.** In Mautic 5/6/7 the GrapesJS builder is built for MJML themes. Legacy themes are only partly editable, and often only in the code view. Make a new email and choose one of the MJML themes (e.g. Brienz, Paprika, Confirm Me, Neopolitan), then double-click a text section. You should get the rich text toolbar.
2. **Site URL / mixed content.** If `site_url` in Configuration → System Settings doesn’t exactly match the URL you use in the browser (http vs https, www vs non-www), the builder iframe can load without its editor scripts. Fix the URL, then clear the cache (`php bin/console cache:clear`) and do a hard refresh.
3. **Browser extensions.** Ad blockers or privacy extensions can block the RTE inside the iframe. Try a private window with extensions turned off.
Also open the browser dev tools console (F12) while you double-click. Any red JS errors there will point to the cause. If you post them here, it’s easier to narrow down.