Are there any Argent fees?
The Lido system applies a 10% profit fee, which is distributed between node operators, the Lido DAO, and an insurance fund. Argent does not take a fee for staking through Lido.
Can I withdraw my stETH once I've staked ETH?
Native withdrawals from Lido will be enabled after Phase 2 of the ETH 2.0 rollout. However you can always trade your stETH back into ETH from the 'Invest' tab. You will receive ETH from the Curve stETH-ETH pool.