Design Meets Code

/* Entfernt die Rundung von allen Bildern im Content-Bereich */
.wp-block-image img,
.wp-block-image {
border-radius: 0 !important;
}
/* Spezifisch für Bilder */
.wp-block-image,
.wp-block-image img,
.wp-block-post-featured-image img {
border-radius: 0px !important;
clip-path: none !important; /* Wichtig, falls eine Maske genutzt wird */
}
/* Globaler Reset für alle Rundungen, die das Theme vorgibt */
:root {
–wp–custom–border-radius: 0px !important;
–wp–style–variable–border-radius: 0px !important;
}
/* Erweitert den Reset auf Beitragslisten und deren Container */
.wp-block-post-featured-image,
.wp-block-post-featured-image a,
.wp-block-post-featured-image img,
.wp-block-query .wp-block-image img {
border-radius: 0 !important;
clip-path: none !important;
}
/* Entfernt Rundungen von den umschließenden Containern in Listen */
.wp-block-post {
border-radius: 0 !important;
}
:root {
--wp--custom--border-radius--s: 0px;
--wp--custom--border-radius--m: 0px;
--wp--custom--border-radius--l: 0px;
--theme--css--wc--border-radius--corner: 0px;
}
[style*="radius:3rem"] {
border-radius: 0 !important;
}

Additional information:

This information is optional, as the above CSS forces no border radius automatically, however, here are some tips on editing border radius you’ve had problems with:

You can disable border radius on images (the theme applies subtle border radius here) by setting it in Appearance → Editor → Styles → Blocks → Image.
Some images inherit the border radius from their container (usually Group block). This is mostly the case with theme sections and layout and you should edit the appropriate template part to get rid of the border radius.

To remove border radius from featured image in post intro, edit “Intro: Post” (and “Intro (Page header)”) template part. The border radius is applied directly on Feature Image block here.

To remove border radius in footer, edit “Footer” template part, where border radius is applied both on Image block (with decorative image) and its Column block wrapper/container.

To remove border radius from featured image in posts list, edit “Posts list item” template part, where the border radius is applied on Group block wrapping around the Featured Image block.

You can access parent (wrapper, container) blocks in block editor multiple ways, such as by using List View.