Versions:

Forge 39.0.79
Starlight 1.0.1 - starlight-1.0.1+forge.36a1c6c.jar

Mod list (±Starlight):

Configured - configured-1.5.3-1.18.1.jar
Controlling - Controlling-forge-1.18.1-9.0+15.jar
FPS Monitor (provides FPS text when not in F3) - FPS-Monitor-1.18-1.0.2.jar
JEI - jei-1.18.1-9.2.1.69.jar

There is a noticeable, albeit slight, performance drop when the latest version of Starlight is installed. I understand this mod's goal is to not increase framerate, however, there is a baseline average drop even when chunks are not being rendered in or out.

I have attached screenshots of some tests I performed. The first set is looking at the same position and standing at the same position after a few minutes of being in the world.

VANILLA:

360 test/viewport movement

STARLIGHT:

360 test

RAM usage is better, however!!! :)

I would need client sparks to identify an issue, given that my local benchmarking doesn't really show anything.