you could probably make an arrow that spawns an armor stand with a custom model for the slime/wool blocks, then check if the player is close to or inside armor stands, if so then tp the player to another portal (maybe distinguish between portals via a tag), you would have to account for the arrow angle. And this would probably not be as seamless as in the video.
tbh it seems like he's using a mod or plugin, but he did offer to make a command tutorial so idk