Vanilla nether portals are just purple blocks. And there is a loading screen when you travel between nether and overworld. Immersive Portals Mod 1.15.1/1.14.4 enhances portals. Now you can see through portals. To go to nether, you just need to walk in.

How to install Optifine with Fabric:
- After installing fabric for 1.14+, you will need to place the OptiFabric mod jar as well as the latest Optifine jar from the official Optifine website into your mods folder.
- Fabric Loader should be the latest version.
Immersive Portals Mod 1.15.1/1.14.4 Download Links:
For Minecraft 1.14.4
Fabric version: Download from Server 1 – Download from Server 2
For Minecraft 1.15
Fabric version: Download from Server 1 – Download from Server 2
For Minecraft 1.15.1
Fabric version: Download from Server 1 – Download from Server 2