I visited 20 years ago and it’s a fantastic place. Unfortunately, I can’t remember much about accessibility, as I was not a wheelchair user at the time. Nevertheless, I remember that my family was bringing a stroller, just in case I got tired. I remember there were a few single steps in the outside paths. Most probably they have solved that by now.
I just did an internet search in Spanish and found a map about the current accessibility status of Alhambra. It seems around 50% is wheelchair accessible (blue trail).
https://www.alhambra-patronato.es/wp-content/uploads/2019/07/recorrido-general-accesibilidad.pdf
The map details type of pavement and slopes too, so it’s pretty good. Seeing that there are many slopes and that distances are big (the estimate time for the whole visit is more than 3 hours), I’d recommend either a power wheelchair or some kind of power assist.
Inside the walled area, there’s a Parador (a state run chain of hotels in iconic places), which, according to their site, is mostly wheelchair accessible. However, as you have the chance to stroll around part of the Alhambra at night, if you stay at the hotel, it’s the most expensive Parador in Spain.
Anyway, I hope it helped a bit : )