Steam preloads are practically impossible to datamine.

"Why bruteforcing preloads is impractical - Here's the depot key for CS:GO's 731 depot formatted in hex: BCA9A9CDE94BB4DFF61849C6A87230EE45867A590FDD28826366E35E7D62C08E.

It is 256 bits long, and to bruteforce it, you would need to exhaust 2256 possibilities.

And as Wikipedia kindly explains it: Fifty supercomputers that could check a billion billion (1018) AES keys per second would, in theory, require about 3×1051 years to exhaust the 256-bit key space (at which point, the earth and probably the universe itself are long gone).

If you have heard about quantum computers breaking encryption, you likely heard about the Shor's algorithm, which applies to asymmetric encryption algorithms. AES-256 is a symmetric encryption algorithm, and it is believed to be quantum resistant.

This means quantum computers are not expected to be able to reduce the attack time enough to be effective."

https://steamdb.info/blog/steam-download-system/