‘The Once and Future King’ by TH White, it has a lot of themes of interest to a Christian and is not explicity anti-Catholic at any points. Here’s a great exchange between a young Arthur and Merlin where the two of them are discussing whether might makes right which is one of the major themes of the book:-
"By the way. You remember that argument we were having about aggression? Well, I have thought of a good reason for starting a war."
“I would like to hear it.”
"A good reason for starting a war is simply to have a good reason! For instance, there might be a king who had discovered a new way of life for human beings — you know, something which would be good for them. It might even be the only way from saving them from destruction. Well, if the human beings were too wicked or too stupid to accept his way, he might have to force it on them, in their own interests by the sword."
The magician clenched his fists, twisted his gown into screws, and began to shake all over.
“Very interesting,” he said in a trembling voice. “Very interesting. There was just such a man when I was young — an Austrian who invented a new way of life and convinced himself that he was the chap to make it work. He tried to impose his reformation by the sword, and plunged the civilized world into misery and chaos. But the thing which this fellow had overlooked, my friend, was that he had had a predecessor in the reformation business, called Jesus Christ. Perhaps we may assume that Jesus knew as much as the Austrian did about saving people. But the odd thing is that Jesus did not turn the disciples into storm troopers, burn down the Temple at Jerusalem, and fix the blame on Pontius Pilate. On the contrary, he made it clear that the business of the philosopher was to make ideas available, and not to impose them on people.”
The reference to Hitler obviously dates it but the points Merlin makes are still worthwhile. Merlin lives backwards through time by the way, I had best mention that it occurs to me as without that context his remarks become confusing.
There’s a book by the German writer Han Bermann ‘The Stone and the Flute’ which is also a book full of Christian themes. Although like LOTR it takes place in a world where Christ is not explicity named. He worked as an editor for an association of Catholic libraries. This book deserves to be far better known to be honest.
Also there’s C.S. Lewis’ ‘Cosmic Trilogy’ which is sometimes considered sci-fi but I’d say it’s more fantasy with a few scientific elements. That’s pretty grim at points though. It’s nothing like Narnia and although Lewis is tackling many of the same themes it’s not written towards children. It also has what I find the most horrifice description of damnation and Satan in the whole of fantasy literature. It’s one of only a very few books to actually manage to scare me. It also ties in loosely with Tolkien’s Middle Earth in the third book via some references. Tolkien also intended Middle Earth to be the distant past of our own world and Lewis builds on that for a couple of references and allusions.