Thinking about it, a holesaw is an expensive way to drill a small one-off hole in timber-derived materials. Frankly a cheaper way would be to get a spade bit, the type with a plain centre point and spurs or nickers on the outer edges of the body, thus:
That's a deWalt 25mm spade bit, but you can clearly see the plain centre point and the spurs or nickers at the outside edges (I use Irwin x4 spade bits for that reason - pre-COVID/Brexit you used to be able to get a set of 16 no of those for just over £20, a bargain). As opposed to that there are bits like this Bosch spade bit with a screw centre point which I find almost uncontrollable, producing a fast but rough hole because the screw point causes them to pull in very quickly:
If you can clamp a piece of scrap wood firmly to the hardboard back of the hardboard it should be possible to drill through from one side only. Alternatively, if that isn't feasible drill through from both sides, as above. Spade bits are designed to be used at high rpm. If drilling from one side only without back support there will invariably be an amount of breakl-out at the back. To minimise this don't push too hard and ese-up as you get to the end of the cut
A problem of using hole saws on timber materials, is that the teeth are very small and the gullets can clog up very quickly. If you allow the gullets to clog up then keep going the hole saw teeth will get very hot, which can draw the temper of the teeth (in other words the teeth will soften and lose their edge - basically they go blunt, even on 3.2mm hardboard if you do enough holes). If they get hot that heat can also transfer into the material you are drilling and scorch it, leaving a brown mark around the edges of the holes in white painted hardboard, for example. So if you do use a hole saw on wood materials, withdraw it from time to time and clean the gullets out - but watch how you do it as the teeth will be hot
BTW,
@mattylad, 20mm holesaws shouild be run at something approaching full speed on hardboard (assuming 1500 to 2500rpm on a cordless tool). Run them at slow speed and they can catch and give a rough edge. When you start to run bigger ones, above about 50mm I find, you need to reduce the speed and use a side handle unless you want to risk a sprained wrist
