SELECT 
  1 
FROM 
  cscart_ec_print_temp_designs 
WHERE 
  session_id = 'PPGA-0G4G-2D7T-7LQZ-DD0R-UJ9S-E7YJ-C3WK' 
  AND product_id = 53 
  AND expires_at > 1770195930 
  AND confirmed = 'Y' 
LIMIT 
  1

Query time 0.00026

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}