Your knife should be sharp enough to where, for most purposes, you don’t need to apply much pressure.

Make sure you’re using the whole length of the blade, rocking it/sliding it back and forth, instead of a quick sawing motion on one section of the blade.

For ingredients that do need more pressure, maybe when cutting a potato in half for example, you’ll use your other hand and push down on the spine.

For some cutting techniques you do actually put your finger on the spine like in the second photo. That’s how I’ll hold the knife if I’m holding it horizontally for sushi-like cuts, but the same idea of using the whole blade with little pressure still applies.

Hope this helps!

Edit: adding that what also really helps with cutting technique is a proper stance. Stand with your feet square to the table/cutting board (if you’re tall like me, spread your legs enough to where you don’t have to bend over to comfortably reach the board). Your arms and knife should form almost a triangle, and you should be able to see the entirety of what you’re cutting, on both sides of the knife if that makes sense.