World Outline is a lightweight shader that barely changes the vanilla style, but adds outlines to it, just like the option in Complementary Shaders.
Preview of the pack
This is great for thumbnails, or simply if you like the look of it. You can customize the look of the outlines in the settings (brightness, thickness, etc.).
Q&A
Q: Is this pack compatible with OptiFine?
A: Yes, this pack is compatible with Iris and OptiFine.
Q: Is this pack compatible with all Minecraft versions?
A: World Outline is compatible with most Minecraft versions (1.8–1.21).
Q: Does World Outline affect entities?
A: World Outline adds outlines to blocks and entities, including players.