<?php
// mu-plugins/theme-features.php
require_once( FEATURES_DIR . '/myfeature.php' );


// mu-plugins/theme-features/myfeature.php
function features_myfeature_init() {
	if ( current_theme_supports( 'myfeature' ) ) {
		add_action( 'some_hook', 'features_myfeature' );
	}
}

add_action( 'wp_loaded', 'features_myfeature_init' );

function features_myfeature() {
	$defaults = [ 'type' => 'foobar'];
	$options = (array) get_theme_support( 'myfeature' );
	$options = wp_parse_args( $options, $defaults);

	//  do stuff
	echo ($options['type']); // qwerty
}



// theme/functions.php
function mytheme_setup() {
	add_theme_support( 'myfeature', ['type' => 'qwerty'] );
}

add_action( 'after_setup_theme', 'mytheme_setup' );
```