I couldn't find a place to change the size of the insertion point, but I finally learn how to change its color. That helps me a lot.
In System Settings, get to Appearance. Next, change "Accent color" to any color you like except the "multicolor" button. When it's set to the multicolor button, the color is overriden by the Pages app, and I couldn't find a way to set it from within the Pages app.
Logically, I tried to change "Highlight color" first, but - and this is screwy - "Highlight color" defaults to whatever "Accent color" is set to and cannot be set independently, even though there's a pop-up menu for doing so.
Sounds like a small bug that escaped the boot heel of Apple.
My System: MacBook Pro, Apple M3, Sonoma 14.4.1