There were many versions of The Animal of Sidon, and the unadapted version might be:
1 The Xerofactor
2. The Cat in the Hat: Although this version also has an adapted storyline, its original author is HP Lovecraft, not Carl Aldern Rex.
3 The Secret Life of Walter Mitty: This version also has an adapted storyline, but the original author is George Orwell.
It should be noted that there may be some differences between these versions, so it is impossible to determine which version is the absolute original version and the version without adaptation.
One common theme is adventure. Since the original story has a lot of adventure elements, fanfics often continue this. Yona and Hak go on quests together, facing enemies and exploring new lands, which strengthens their bond.
You can also try FanFiction.net. It's one of the oldest and largest fanfiction platforms. Just use the search function and type in 'Link x Sidon' to see if there are any relevant stories. Additionally, some Zelda - specific fan communities or forums might have links to or even host their own fanfictions of this pairing.
I'm not sure specifically about a large quantity of Link x Sidon fanfiction. However, you can start by checking popular fanfiction websites like Archive of Our Own. There might be a decent number of stories featuring this pairing depending on the popularity of the characters within the fan community.
Yes. The Yona of the Dawn manga has ended. Although it might be sad for fans, it left a memorable impression with its engaging plot and characters throughout its run.