So I recently finished NRLW and I put together a new workout plan for myself, but I could use some advice. Are there any muscle groups that I'm missing entirely? Anything I'm doing that's redundant?

Here is my plan:
Tuesday
3x10 squats alternating with
3x10 push-ups
3x10 lunges alternating with
3x10 dumbbell rows (one arm at a time)
3 planks, gradually increasing time

Thursday
3x10 lat pull-downs alternating with
3x10 bulgarian split squats
3x10 YTWL (from NRLW) alternating with
3x10 single-leg deadlifts
3x10 swiss ball jackknifes

I feel like I should be doing regular deadlifts in there somewhere, or like my Thursday routine has too much back stuff. Any suggestions? I'm doing this in addition to triathlon training so I'm also running, biking, and swimming.

Looks good.

If you want to do regular deadlifts in there, I would put them in place of the single leg deadlifts or if you feel that the regular deads would give you too much back work a bilateral hip dominant movement such as pull-throughs would work too. For most people, replacing the single leg deads in this manner would be what I would suggest as you already are getting some unilateral lower body work on both days. However, in your case, as you are training for a triathalon, and extra emphasis on single leg work is probably better.

Your question was if you missed any muscle groups, but since you have done NROLW, you might want to think more in terms of what they preached. Did you miss any movement patterns? You covered everything pretty well. You could perhaps work in a vertical push. However, most people could use more pulling than pushing anyway, so I think you are fine and it gave you the opportunity to get in some shoulder prehab work with the YTWL's.