None of the published settings books for 5th Edition mention the use of 10th level spells by that name, but unusually powerful spells still exist
There are no mentions of 10th level spells. Instead the lore refers to spells of great power in more generic language, for example, Rime of the Frostmaiden refers to a "spell of unparalleled power" that Karsus attempted to use to usurp Mystryl (thanks to @Carcer). So the concept that there can be unusually powerful spells has not been changed, but this is not expressed in spell level terms any more.
You can technically cast 10th level spells using the Book of Exalted Deeds, but in lore, the concept of 10th level spells in that language is not used.