Maybe this will help:

https://www.musictech.net/tutorials/fl-studio-tutorial-midi-1/

Also google/bing MIDI recording in FL will bring up other tutorials.

Mike and I are saying the same thing in that you have to set up the MIDI channels in both your keyboard and FL.

Note that depending on your audio/MIDI interface you can record 16 or more channels simultaneously, but you would need that many different MIDI inputs and players!

Have you tried my original suggestion? That is how I record MIDI, usually one track at a time. If JonD or BobH are here I can record two different MIDI track simultaneously. OR if you can split your keyboard into different zones then you can record 2 or more MIDI tracks with different channels simultaneously.

Here is how record MIDI when I'm alone. Track 1 MIDI channel one I may put down a bass line. Track 2 MIDI channel one I might put down a piano line, etc. Note that because I am using totally different tracks and sounds I can use MIDI channel 1 again as the tracks will not interfere with each other. As Mike indicated MIDI channel 10 is reserved for drums.

I'm no longer allowed to go caroling at the psych hospital.
I guess Do You Hear What I Hear was a bad song choice!

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware