So many parents struggle with their child falling asleep and staying asleep. Many sources will recommend melatonin. Let me start by saying, I am in no way a medical professional, and any medical advice should come from your pediatrician. Melatonin can sometimes help families get back on track with sleep, and I have seen children on medication for ADHD or with cognitive disabilities benefit from melatonin at bedtime to help calm and relax for sleep. That being said, it often is not the fix all answer families are looking for and in my experience can cause more middle of the night wake-ups.
Typically around age 2, your child's sleep will change, but I would not at all label this a regression. A regression is something that doesn't need to be addressed and will simply go away in a week or two, what is happening with your toddler is likely not this.
The answer most sleep consultants won't give you is- your child needs to fall asleep independently at bedtime. Once your child can fall asleep at bedtime, they will be able to sleep through the night. If you are shaking your head like that could never happen, my child is too crazy at bedtime and doesn't seem tired at all, there is a good chance they are actually overtired. Try moving your child's bedtime closer to the 7/730pm time. Work on creating a relaxing bedtime routine that is consistent each night. We want your little one to know sleep is coming so their body can get ready and start calming down. Be the leader of their bedtime routine, set a boundary and stick with it. I recommend bath time every night followed by two short books or one long book, no more. Tuck them in, rub their back for 1-2 minutes, then leave the room and give them the chance to fall asleep independently.
When I begin working with a family wanting to sleep train, the first thing we will do is stop use of melatonin. When your child is learning to fall asleep on their own, they need to be aware they are able to do it without assistance- this will lead to them being able to stay asleep in the middle of the night. Part of the reason your child wakes in the middle of the night is due to sleep cycles. Our bodies naturally wake-up in the middle of the night as we transition from REM sleep back to falling asleep. If our children don't know how to fall asleep without a parent in the room at bedtime, they won't know how to fall asleep in the middle of the night without their parent.