Yes, ordered a Mazda in August and had to pay a £250 deposit. It was unexpected, but I guess it’s to stop people from ordering and then cancelling since you have already made a commitment.
You can still cancel and you would be able to get any deposit back. We don’t buy the car, Motability Operations do. Consequently, even if you sign paperwork at a dealer, you are not entering into a legally binding contract with them. The only time you do that is when you enter the PIN when you accept the car, as that enters you into a contract with Motability Operations. I’ve never cancelled an order myself, but many on this forum have. Some dealers may huff and puff and one or two have been slow to refund, but when challenged they always do. In the current climate, the dealer would probably be quite happy as even if they couldn’t cancel the order they could sell it to a private customer at far more profit!