How can I make text appear bolder (as shown in these images)?

Currently, I am instantiating a text prefab that looks like this:

If I instantiate multiple of the same prefab, the objects stack and look like this:

How do I get a single prefab to look like the second image? I don’t want to instantiate 3-5 prefabs at a time just to make the text as dark as I would like. The alpha values of my text and outline are 255.

You could always add a shadow to the text, it would define it much better, and you can even use a shadow of the same color as the text, to simply expand the text visibility.
You can also adjust Line Spacing, so you can make it as bold as you like, up or down.

Text prefab are a thing in Unity. For some reason they show blurry (there must be an explanation).

The easy way to sharpen your text is to scale the object down and increase the font size.

If you are using the UI system, you decrease the canvas size, somewhere down to 0.001 is often ok. Then increase the Dynamic Pixel per Unit in CanvasScaler to 10 or more.