Minecraft's mod collection is ever-expanding, and Immersive Portals is a great pick for players who want their portals to feel a little more like portals.

The second mod used by OP is called Pehkui, which can minimize the size of entities. Redditor u/jumbledFox combined Immersive Portals and Pehkui to create this impressive illusion.

Transform glass into functional mirrors, then combine them with immersive portals to step into a mirror world! This mod adds a unique twist to Minecraft.

Immersive Portals is a mod that was originally released back in 2019, but it's been updated frequently since. The mod relies on Fabric API, and it adds a few nifty features.