'Cleansing' or 'detoxing' smoothies are marketing — the body cleanses through liver and kidneys without help from specific drinks. Many such smoothies contain more concentrated sugar (from fruit) than actual benefit.
What works instead
Adequate water daily. Whole fruit and vegetables (with fibre intact). Adequate sleep (most 'detox' is liver work that happens overnight). Limited alcohol.
Where smoothies can be useful
Increasing vegetable and fruit intake when whole-food versions feel hard. Post-workout protein delivery with carbs and micronutrients. Convenience for time-poor mornings.
Skip the 'cleansing' marketing. A real smoothie (protein base, one fruit, vegetables, healthy fat) can be useful nutrition. The 'detox' framing is marketing without nutritional foundation.