I visited this WHS in July 2020. I had skipped this WHS on my last trip to Andalucia to avoid having any 'fatigue' from the sort of Golden Triangle of Spain - Granada, Cordoba, Seville. This choice turned out to be a wise one as all three cities have quite a lot to see and visit and are really top sites. Of the three, I rated Seville's inscribed sites slightly less than the grandiose Granada and amazing Cordoba.
The Cathedral's highlight is undoubtedly the recently restored Giralda Tower (top left photo). Currently, due to the COVID-19 restrictions, both can be visited with a longish tour with a maximum of 50 people. I enjoyed the views of the tower from the several nearby plazas. Make sure to visit the Prince's Gate and the Door of Forgiveness in the afternoon too. The Spanish Renaissance General Archive of the Indies (bottom left photo) nearby is the repository of extremely valuable archival documents illustrating the history of the Spanish Empire in the Americas and the Philippines (closed on Mondays).
Last but not least, the Alcazar is most probably Seville's highlight, yet it was no match with Granada's Alhambra. The level of Moorish architecture detail in general is more on the level of the Mudejar architecture of Zaragoza's Aljaferia especially when gazing at the marvellous Patio de las Doncellas. A lot of the Alcazar was changed after damage by the 1755 Lisbon earthquake. For example the façade of the Palacio Gótico overlooking the Patio del Crucero was completely renovated using Baroque elements and as such the palace together with most of the Alcazar and gardens (bottom right photo) now present a unique blend of styles. The definite highlight of the Alcazar, worth the trip alone, is the Hall of the Ambassadors (top right photo). A walk from the outside of the Alcazar, especially along the Callejon del Agua and the Santa Cruz neighborhood, is worth having.
All three inscribed buildings have a metal UNESCO inscription plaque on the wall. Seville has much more on offer than the three UNESCO inscribed buildings and deserves at least 3 nights to explore at leisure.