Earn lets eligible dollars (USDC) in your wallet earn rewards.
Earn is off until you turn it on. When it is on, Ulys deposits your eligible USDC into third-party onchain lending protocols, within the permission you approve.
The app shows the current rate. The rate changes and can go down.
Rewards come from the third-party protocols, not from Ulys. Your USDC is not a bank deposit and has no deposit insurance. A protocol can fail, and you can lose funds.
You can turn off Earn at any time.