Difficult one only made worse as its your first car on the scheme. I’m afraid only you can decide what to do. If it were me who needed an electric tailgate and heated seats for my health conditions rather than for the sake of having them. I wouldn’t except the vehicle.
You could ring Motability and say if I accept it could you have an early termination when one more suitable for our needs becomes available. Or you could decide to keep your current vehicle if you still have it, untill the situation manufacturers improves and rejoin the scheme later on.
You could look at a Tuscon its been on the market longer than the Sportage and a greater chance of one being available (someone on here got one in 10 days after they cancelled their current order albeit a base model.) You may need to travel or ask your local dealer to check UK stock. The Tuscon is essentially a Sportage wearing a different coat, but the interior isn’t quite as posh looking.