Quick and dirty slow mo effect Gamemaker

// oliver @pixelchipcode
//create
// Default frame rate settings
default_fps = 60;
target_fps = default_fps;
change_speed = 1; // Speed of transition (higher = faster change)
current_fps = default_fps;

// Set the initial game speed
game_set_speed(default_fps, gamespeed_fps);

//step
if (mouse_check_button(mb_left)) {
    // Set the slow-motion target frame rate on mouse press
    target_fps = 10; // Example: Slow motion at 30 FPS
} else {
    // Reset to the normal frame rate on release
    target_fps = default_fps;
}

// Smoothly interpolate the current FPS towards the target FPS
if (abs(current_fps - target_fps) > 0.1) { // Only adjust if there's a noticeable difference
    current_fps = lerp(current_fps, target_fps, change_speed * delta_time / 100000);

    // Clamp and round the FPS to ensure valid values
    current_fps = clamp(round(current_fps), 1, 1000); // FPS range: 1 to 1000

    // Set the game speed
    game_set_speed(current_fps, gamespeed_fps);
}