The bug:
After manually adjusting the Gamma from options.txt in the game's files above 1.0, snapshots do not follow the new Gamma level, but instead revert it back to 1.0 automatically. 

Note that official releases (e.g. 1.18.2) work with Gamma above 1.0.

How to reproduce:
1. Navigate to the following in your files browser: C:\Users\YOURUSERNAME\AppData\Roaming\.minecraft\options.txt
2. Edit the Gamma level to above 1.0.
3. Load 22w16b from the Minecraft Launcher.
4. When you play in a world, the Gamma level will automatically be 1.0 despite tweaking it manually beforehand. To check, quit the game and go back to options.txt. You can see that the Gamma is in fact back to 1.0. The world at nighttime is also visually darker than what a Gamma level above 1.0 should be.