[tabifolk]

According to Cory Lee it is fairly wide open, but not much more in terms of a description.

https://www.curbfreewithcorylee.com/2014/12/04/wheelchair-access-bangkok-thailand/

According to wheelchairtraveler.org,

The palace grounds are partially open to the public and are a must-see attraction for visitors to Bangkok. The lawns and gardens are wheelchair accessible.

But he also goes on to say that the Temple of the Emerald Buddha only has steps.

https://wheelchairtravel.org/bangkok/attractions-sights/

Hope this is helpful to get you started.