Headcanon that tea is enjoyed in every province in Tamriel, but they all prepare it differently.
Breton and Imperial both tend to like their tea black with occasional cream and/or sugar. Their tea cultures probably look nearly indistinguishable to outsiders, but there are subtle differences that they each think makes them superior to the other.
Khajiit enjoy strongly spiced powder teas ceremonially sweetened with moon sugar
Much to the horror of Bretons and Imperials, both Nords and Orcs prefer their tea salted and frothy with milk and butter
The Altmer have an extremely complex tea culture, especially in the higher levels of society. It can take an entire human lifespan to learn the more advanced art form and understand the social politics that can accompany it.
The Dunmer have a truly unique taste that is seldom appreciated beyond those that grew up with the culture. They like their tea very strong; sometimes bitter, sometimes spicey. They are one of the few peoples to regularly incorporate powdered mushrooms into their teas.
Redguards, like the Khajiit, enjoy sweet spiced tea, but like the Nords and Ocrs, they also have a version of buttered or 'fatted' tea that is renowned across the continent for promoting endurance. It was developed as a staple for long cross-desert journeys
Bosmer also enjoy tea, but it's notably different from all the other provinces in that the tea leaves can only be harvested after they fall naturally. Sometimes the tea is even brewed in unsalted bone broth to make the beverage more sustaining. Foreigners are often warned away from sampling Bosmeri teas as the Wood Elves have a unique resilience to certain toxic leaves and berries they use for added flavor.
Feel free to add on or make use of these headcanons!