EIP-4399: How to use PREVRANDAO in evm?

EIPs
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1

I didn’t find the documents about how to use random source in evm using solidity?

Is there a way to access the randao number in a specific block just like the funtion: blockhash(uint blockNumber) returns (bytes32)?

2

Yes there is, although not yet for a specific block (or slot) number. See EIP-4399: Supplant DIFFICULTY opcode with RANDOM and also Solidity Deep Dive: New Opcode 'Prevrandao' about this.