I'm using the 1.18.2 Forge version of the mod and I plugged in my MIDI controller. Everything seems to be working, however there is a small delay between pressing the key and the note playing. If I play on my PC keyboard, there is no latency.

Is this normal? Or is there something I can do to reduce the latency coming from using a MIDI keyboard?

Hey there! Sorry to hear this!

Unfortunately, I don't really have a way to diagnose this issue, even if you were to send your logs... :(

Maybe your PC is low-end? Perhaps you could try closing some background apps?
Have you tried restarting your computer? (Not simply turning it off then on.)

If all else fails, I'd recommend getting a software like LoopMidi to hopefully instantaneously detect your MIDI, and then play it in Minecraft.

Attached here is a tutorial for that.

This is just one of many MIDI loopback softwares, I just happen to be familiar with this the most.

Other than that, I'll be closing this issue—because I really am just unable to help you... This is outside of my capabilities :')

Do keep me posted if you succeed, though :D