Replace File-Upload output with an icon that matches the file type.

gv_iconify_fileupload_output.php

<?php // DO NOT COPY THIS LINE

/**
 * Replace File-Upload output with an icon that matches the file type.
 *
 * @see https://github.com/GravityKit/GravityView/blob/a6584d8a/includes/fields/class-gravityview-field-fileupload.php#L455
 * @filter gravityview/fields/fileupload/files_array
 *
 * @param array $output_arr Array of files, one item per uploaded file.
 * @return array Modified array with icon-only output.
 */
add_filter( 'gform_secure_file_download_location', '__return_false' ); // Filter necessary to output the full URL of uploaded files
add_filter( 'gravityview/fields/fileupload/files_array', 'gv_iconify_fileupload_output', 10 );
function gv_iconify_fileupload_output( $output_arr ) {

	// Map extensions ⇒ Dashicon classes.
	$icon_map = array(
		// Images
		'png'  => 'dashicons-format-image',
		'jpg'  => 'dashicons-format-image',
		'jpeg' => 'dashicons-format-image',
		'gif'  => 'dashicons-format-image',
		'webp' => 'dashicons-format-image',
		'svg'  => 'dashicons-format-image',

		// Documents
		'pdf'  => 'dashicons-media-document',
		'doc'  => 'dashicons-media-text',
		'docx' => 'dashicons-media-text',
		'rtf'  => 'dashicons-media-text',

		// Spreadsheets
		'xls'  => 'dashicons-media-spreadsheet',
		'xlsx' => 'dashicons-media-spreadsheet',
		'csv'  => 'dashicons-media-spreadsheet',

		// Archives
		'zip'  => 'dashicons-archive',
		'rar'  => 'dashicons-archive',
	);

	foreach ( $output_arr as $key => $file ) {

		$url  = $file['file_path'];
		$ext  = strtolower( pathinfo( $url, PATHINFO_EXTENSION ) );
		$icon = isset( $icon_map[ $ext ] ) ? $icon_map[ $ext ] : 'dashicons-media-default';

		// Build the HTML the View will render.
		$output_arr[ $key ]['content']  = sprintf(
			'<a href="%1$s" class="gv-file-icon-link" target="_blank" rel="noopener noreferrer"><span class="dashicons %2$s"></span></a>',
			esc_url( $url ),
			esc_attr( $icon )
		);
	}

	return $output_arr;
}

/**
 * Make sure Dashicons are available on the front-end (they already are in admin).
 */
add_action( 'wp_enqueue_scripts', function () {
	wp_enqueue_style( 'dashicons' );
} );

Where to put this code

Read here on where to put code snippets: https://docs.gravitykit.com/article/210-where-to-put-code-samples

Styling (optional)

.gv-field-file-uploads{
	margin: 0 !important;
	padding: 0 !important;
}

.gv-file-icon-link .dashicons {
	/*font-size: 28px;       /* Bigger icon */
	line-height: 1;        /* Remove extra space */
	vertical-align: middle;
}

.gv-file-icon-link:hover .dashicons {
	opacity: 0.7;          /* Simple hover feedback */
}

/* Remove underline from the icon links */
.gv-file-icon-link {
	text-decoration: none !important;     /* no underline */
}

/* Keep it from coming back on hover/focus */
.gv-file-icon-link:hover,
.gv-file-icon-link:focus {
	text-decoration: none !important;
}