I absolutely love the look of this shader, and it's become my go-to when playing Minecraft, full stop. It would be very cool to see an option in the config UI for shadow resolutions beyond the current "high" setting, since shadows still look quite pixelated even on the higher settings.

My current shadow settings and what said settings appear as in-game.

Before trying to use higher resolutions in the shadow map, I would recommend changing the "Shadow type" setting to "Filtered" and leaving "Shadow Blur" at 2.0.

There is no power on earth that can show a shadow without jagged edges without filtering it. It would have to be absurdly large.
You cannot have both a highly defined shadow and no jagged edges at the same time in a shadow map without making it enormously large. Filtering is necessary to mask this.

If you're having issues with edges on more distant objects, try increasing the shadow distance. The shadow loses resolution with distance, and this reduces the rate at which that resolution decreases.

Don't worry that the shadow definition will decrease when increasing the distance. The shader is made in such a way that the resolution increases in the same proportion as the distance, so the pixels are the same size in practice.