Of course you can't transfer bookings to a new owner that would be highly unfair on your guests who booked your listing in good faith based on YOUR reviews and the way you run things @David-and-Gael0 You are not selling 'an airbnb' you are selling a property. Listings are not transferable. The new owner may want to price and manage the property differently.
Really this is something it would have been better for you to look into before you put your house on the market.
If you are selling your property you should have just opened up your calendar three months in advance so you didn't accept bookings you knew you couldn't honour. This is what I did and the new host set up a listing to start from when they had ownership of the property.
The advice from Airbnb was correct if you cannot honour the bookings you need to cancel them and they can rebook should they wish with the new host. You cannot expect guests to necessarily book with an unknown host.
Advise the new owner to set up their own listing (if you want to can give them access to your photos and copy to use, do so) once the purchase is complete, they can let their listing go live.
The only way around this that I can see is if the new owner blocks out dates from his calendar for existing bookings. You can continue to host these dates from your listing and agree a co-host commission. (you would need to draw up a contract with the new owner to cover this. Of course the risk is if he doesn't maintain the property you could end up getting bad reviews.