How to remove the Featured Image from individual posts?

Create an override theme folder (https://getpublii.com/dev/theme-overrides/). Copy the config.json file into it.
Open the config.json file in your override folder using your preferred editor. Look for “postConfig” and edit the “featuredImageWidth” section so that it looks like this:

"postConfig": [
    { 
    "name": "featuredImageWidth", 
    "label": "Featured Image Width", 
    "value": "post__image--wide", 
    "type": "select", 
    "options": [ 
    { 
    "label": "No Image", "value": "post__image--none" }, 
    { 
    "label": "Normal", "value": "post__image--normal" }, 
    { 
    "label": "Wide", "value": "post__image--wide" }, 
    { 
    "label": "Full", "value": "post__image--full" } ] },

The essential part is { “label”: “No Image”, “value”: “post__image–none” }.

Next, you need to add custom CSS in the Publii app (Tools & Plugins > Custom CSS):

.post__image--none { display: none; }

Once you’re in the post editor, you’ll see an option for the Featured image to display “None” images