Yes, you can study in English
Many foreigners do not realize they can prepare for the theory exam with English study material and, in some cases, take the exam with language support. The exact availability depends on the testing center and local administration, so it is worth confirming in advance.
Even if you study in English, you are still learning Spanish traffic law. That means you need to understand local concepts such as roundabouts, right of way, urban speed rules, and required documents.
Where most learners struggle
The main obstacle is usually not English itself but mental translation. Many learners understand everyday English, yet struggle when questions use technical wording or describe a typical Spanish driving situation.