Hi @roger-vikstrom, the Featured Image block has a setting for opacity that you’ll need to adjust in your Single template.
Go to Appearance > Editor
At the top of your page, click the template selector and then click “Browse all templates”
That should bring you to the Templates area of your site. You can also get there by visiting:
https://www.rvbild.se/wp-admin/site-editor.php?postType=wp_template
Click “Single” to access your single post template.
Select the Featured Image block placeholder
In the Settings panel on the right, drag the Opacity slider to 0, or type 0 in the Opacity box, as you see here:

Let us know how it goes!