I can't hear my midi controller

I'm trying to get Logic Pro X to set up to work with a StudioLogic SL88 midi controller, and a Focusrite Scarlet Solo (3Gen). When I create a new midi track, say with a Grand Piano, I can see the input when I play it, but I can't hear it.

My setup was working well with Garage Band and with Presonus Studio One.

I've read several support articles on this issue, and none of them work for me. I've verified that the Audio Input/Output is set correctly in Settings. I've verified the Scarlett Solo monitoring is working (I've successfully played YouTube videos using Scarlett Solo as an output). I've made sure software input monitoring is on and made it so even non-selected channels monitor through Logic Pro. I've tried setting the Output Device to Built-In Output. None of this works. I've verified the volume levels are set up correctly.

Whatever I do, I can see the input, but I can't hear it.

I'm pulling my hair out. What on earth is going on? This is so basic.