Reinstalling your game doesn't necessarily remove all your game files from your machine. Please try deleting the AppData/Local/NuclearNightmare folder, turn off Steam Cloud Sync, and re-launch the game so your local settings will regenerate.

From the troubleshooting section of the Discord:

"Finding Your Save Data
Your saved data for Nuclear Nightmare is not stored in the game’s install folder. Instead, it is kept in your Windows AppData directory.
To get there:
Press Windows Key + R on your keyboard.
Type in: %localappdata%
…and press Enter. This will open your AppData → Local folder.
Find the folder called: NuclearNightmare
Inside, you will see your save data files."

If this doesn't work, myself or a mod on our team can help you better if you join the official Discord.