This members-only tutorial provides the steps to set up category and tag archives in Oxygen such that the latest 3 posts from the current category/tag appear at the top with the rest offset by 3 at the bottom in another section while ensuring that pagination continues to work.
We shall display the archive description above the bottom grid of posts.
While the tutorial shows Easy Posts being used, you could use Repeaters if you wish, although that is not something I recommend due to duplicate IDs problem.
If you would like to show categories and tags for each post with more control than what is possible by default in Oxygen, implement this tutorial.
Let's create an Oxygen Template that applies to all category and tag archives.
Edit it with Oxygen.
Add a Section and add a heading. Double click to select the text > Insert Data button in the top toolbar > Archive Title.
Add another Section for showing the first 3 posts in the current category/tag.