Please describe the feature you'd like to see added.

a CLI parameter that makes TP send SetNewPrevHash with a custom nbits/target

Is your feature related to a problem, if so please describe it.

testnet3 and testnet4 are pretty much broken for any meaningful mining-related testing

however, SRI official tutorial points users towards testnet4, which recently that got @jakubtrnka quite confused

while the custom signet approach is a viable alternative, it's not scalable for a replacement of testnet4 on the official tutorial

Describe the solution you'd like

the solution (originally proposed by @jakubtrnka) is to adapt the tutorial for mainnet, while modifying the SetNewPrevHash messages coming out of TP so that they carry a custom difficulty

that would allow SRI software to still mine "valid" blocks under somewhat realistic conditions

Describe any alternatives you've considered

custom signet, although that has the drawback of someone joining with a powerful ASIC, raising the network difficulty to really high values and leaving the network unsuitable for anyone that doesn't have similar hashpower available

Please leave any additional context

No response