Continued on from here.

I agree it may not be by much depending on mass.

No disagreement here. I was discounting it due to the low acceleration in this case (e.g. 1e-8) being essentially immaterial to the calculations. But in this case, yes, it does accelerate. We could at the moment the filament is pinched also fire up a 1N rocket motor to counter the force, killing the tiny acceleration. We could also make the mass arbitrarily large, but then it would have non negligible gravity and the calculations for how far the mass moves in any given time and it's energy become somewhat trickier.

Yea sure will.

OK, so we have our 20,000,000 J each second.

Let's swap it round. The filament is fixed to the very large mass, and you (a tiny you of negligible mass) are riding on the 1Kg mass as it accelerates. The you pinch your fingers to exert 1N of drag and you and the mass's acceleration stops (or close enough!) as the 1N of rocket engine is countered by the 1N of drag.

As before, the 20,000,000J each second is going into your fingers.

Agreed?