Nap time struggles

Me

We're transitioning between 2 naps down to one and can't seem to find the balance. He wakes up between 8 and 8:30 everyday and usually goes down for a nap between 11:30 to noon. He'll sleep for 2 sometimes 2 1/2 hours. Then around 5pm he acts like he wants to take another nap but if I let him do that he's up until midnight or later. In fact if I put him to bed anytime before 8:30 he wakes up a couple hours later like he took a nap then we're up all night 😭 but if I don't let him take a nap he gets overtired a huge grouch! And regardless of what time we go to bed he wakes up at 8. I need tips, how do I fix this?