I have a power contract that is pre-paid for more power than I actually use in the winter time; and so just leave most of my electronics on to serve as "free" space heaters (all power ultimately ends as heat, even lights etc).  Including my PC. So can I turn that into money?  

Looks like yes.  And here's a link on routes to get revenue from running a PC that would just be idled anyway.

https://millennialmoney.com/get-paid-to-leave-your-computer-running/

BUT

I have 2 concerns/priorities that hopefully those more familiar can guide me?

1) I don't want to ever own or possess crypto.  There are tax implications/alerts that are triggered by that.  I'm totally fine letting someone else pay me to run the processing power for them to generate crypto, and they just pay me money to churn; so long as I'm able to answer Question#1 on my 1040 as a NO, on if I have ever owned or traded cryto.  Do any of these systems work that way, or will I at some point actually have cryto?  (here's the 1040 line: "At any time during 2022, did you (a) receive (as a reward, award, or payment for property or services); or (b) sell, exchange, gift, or otherwise dispose of a digital asset (or a financial interest in a digital asset)?"  My suspicion is the answer to that may not be NO, if I run the system as a crypto generator - but it's not clear, so ... maybe?

2) Some of the other usages I have concern could have nefarious and potentially liability issues.  I'd hate to just rent-out my processing/HDD space, and end up with something heinous and wildly illegal in my possession, as the processor/renter.   Not sure if any thoughts on that?

Are there any other "guaranteed clean" routes to generate revenue from an idle PC?

Its an interesting question, I don't have any good answers but I would be interested to see what comes up.
I would think that you could answer no as far as crypto ownership goes with some of those options, but I am not sure.  Dealing with gov't isn't always clear, unfortunately.