I've found my sleep regularity to be pretty malleable. It can become a habit. When I was in grad school I went to bed at midnight and woke up at 7am. Once I started running more in the mornings, I gradually shifted to going to sleep at 9pm and waking up at 5am.
The first couple days or week will feel pretty bad, but if you give yourself enough time then you'll shift your sleep schedule around. Now I get tired at 8:30pm and fall asleep at 9ish like clockwork. grad school me would have considered that insane considering I'm doing less work on average during the day. My day is just shifted now so that I do more stuff in the mornings and really relax in the afternoons, which is the opposite of before.
A key is actually giving yourself enough time to fall asleep. Most people think they can hop into bed and just get 8hrs, when you actually need to hop into bed around 30mins beforehand and really relax with a book or something.
I also think it's important to not stress about sleep a lot. Unless you're literally feeling miserable or have apnea, I think it's better to just let yourself relax if you wake up in the middle of the night. Sometimes I'll snap awake at 2am and just read for 2hrs, then get 2 more hours of sleep and generally feel fine.
The only way I really made an early wake up work was wearing amber safety glasses to block blue light for an hour or two before bed every night.
I will note that if you feel absolutely terrible on 8-9 hours of sleep, you should check with a doctor about it. I have hypothyroidism and was on too low a dose of medication, and felt so tired after work that I almost drove on the wrong side of the road. I'd thought this was simply from moving my sleep schedule and getting less sleep after starting a new job, but I got a blood test for unrelated reasons and found I was hypothyroid. A couple weeks after starting the new dose of medication and I feel like a new person.
People are different. What you find easy and trainable, someone else will find it doesn't require training and someone else will try as hard as they can and won't succeed.