I check the Kindle Spanish charts pretty regularly, and romance absolutely dominates. It feels like every time I look, the top twenty is flooded with contemporary romance, steamy novela-style dramas, and those addictive billionaire romance sagas. Historical romance set in various Latin American periods also does really well.
Thrillers and crime fiction are the other massive category. Spanish translations of Nordic noir stuff find an audience, but the homegrown 'thriller negro' from Spain and Latin America seems even hotter. Think dark, socially-conscious crime plots.
Beyond that, self-help and mindfulness titles have carved out a huge permanent space. You'll always see a few books on personal finance, habit-building, or spirituality hanging around the top fifty, which suggests a practical, non-fiction reading habit alongside the fiction.