Add Alt-text to the image on author box

Edit the element used to display the author meta. Select the image block for the author image and add this class under Advanced > Additional CSS Classes field: ac-add-link-aria-label

Then add this PHP:

add_filter( 'render_block', function( $block_content, $block ) {
    if ( !is_admin() && ! empty( $block['attrs']['className'] ) && strpos( $block['attrs']['className'], 'ac-add-link-aria-label' ) !== false ) {
		$myreplace = '<a';
		$myinsert = '<a aria-label="' . get_the_author_meta( 'display_name' ) . '" ';
		
        $block_content = str_replace( $myreplace, $myinsert , $block_content );
    }

    return $block_content;
}, 10, 2 );