[EDIT] FFS, curseforge and github are the opposite of intuitive, there already is an experimental version for sodium (still doesn't work with Starline).

Well, the Starline Iris and Sodium are still in development, highly unstable and etc. So something like this is expactable.

Minecraft 1.16.5
Immersive Portals 0.99
Iris 1.1.2 Starline build 470 - https://github.com/HyperCubeMC/Iris
Sodium 0.2.0 IRIS3 build 119 (made for Iris Starline) - https://github.com/HyperCubeMC/sodium-fabric

Issue on Sodium's GitHub page: HyperCubeMC/old-starline-sodium-fabric#4