This is a Netflix TV series that they released in March 2020, but it has a very long history. The original, much acclaimed book is De brief voor de koning, a 1962 Dutch children's book by Tonke Dragt. I'm interested to find that the book apparently didn't have any magic at all: it was a medieval coming-of-age tale.
Tiuri is the young adopted son of Sir Tiuri the Valiant - he and his mother were refugees from Eviellan. Tiuri now faces the trials for knighthood, although it's quite apparent his combat skills simply aren't that good. Nevertheless, he makes it to the final stage with four others - only to break the rules of the trial because of his compassion, which causes him to leave on a quest to deliver a letter. He's pursued by multiple people from three or four different political entities.
The series focuses almost entirely on the young knights, and a couple friends acquired along the way. The series is blunt about the reality of kingdom and royalty politics, showing that marriages are purely political and as a result, kings and queens are likely to have a lover they actually like on the side - I have no issue with this, but it's an uncommon attitude for a children's show/book, and contrasts vividly with the lack of reality in the death count: one child hero dies in the entire series.
The acting is uniformly mediocre. There are too many reversals of loyalty, and too much rushing about. There's no coherent model for the magic, and no explanation - particularly not of the odd "look who's the magic wielder" change toward the end of the series. Knowing the magic was tacked on, it absolutely feels like an unnecessary extra. I also have to think that the (surprisingly charming) young gay romance didn't exist in a children's book in 1962. While it certainly looks pretty, the series is kind of sloppy and too long for what it achieves.
As a small tidbit for Canadians watching the series, the song that the Novices whistle a couple times through the series is the wonderful "In Hell I'll be in Good Company" by The Dead South (although the series doesn't use Dead South's lyrics).