The IRS has no official guidance on the taxation of staking rewards that cannot yet be withdrawn, but some investors are arguing that where withdrawals of staking rewards are restricted, for example ETH 2.0 staking rewards, that they should not pay tax on this. There's some merits to this argument, but the conservative approach is to report all staking rewards as income regardless of whether you may withdraw them immediately. If you're unsure, or want to take a more aggressive approach, you should speak to an experienced crypto accountant for advice.