This kind of thing has been proposed but you can easily end up in a situation where the device uses 2c of electricity to mine 1c and then you'd be better off preloading the device with, say, ten years worth of currency instead of mining.

On a CPU it’s gonna be dollars or electricity.

The whole point of profitable mining is to build asics such that the cost of electricity gets lower than the mining rewards.

21 was pitching IoT ASIC mining and it still looked like a waste of electricity.

Like what? If you have anything my computer can do to generate 1c/10seconds with no input from me, that’s $3.60/hour income running twenty four seven; I’ll buy a few and retire right now.

Computers have costs associated with running them. electricity, infrastructure for them to run. The cost is not zero.

Even at the height of the crypto boom my computer with a very fast graphics card at the time made like ten bucks a day.

Is it still generating money for you? Still $10 / day?

Nope, not making enough to be worth the power drain and the noise anymore.

LE certificates last 90 days. $3.60/hour is enough to cover renewal for almost a million certificates. The mining doesn't have to be done during the renewal process. You can do the mining gradually between renewals.

I'm not a bitcoin person, but...

I don't think you can mine $0.01 worth of bitcoin. Most of the time, you'll lose the race to find the correct hash collision and so you'll end up with nothing. Other times, you'll win and get the reward for the block which is 12.5 BTC at the moment (IIRC). People do join collectives to pool their mining power, but there isn't predictability to when the collective will end up with a coin. If you're looking to set up a web server, you don't want to be waiting days or weeks or whatever while your collective tries to win a block. Theoretically, you could buy a lot of computing power and always get unlucky.

So you can't really get a penny of bitcoin via mining.

Realistically, larger pools mine multiple blocks per day and can pay out daily. 21 even came up with a scheme to front BTC to the device and make it up later, but that's excessively complex IMO.

you can join a mining pool.

But mining once cent worth of bitcoin would cost you multiple dollars on a CPU.