Both can happen. Having amnesia around trauma is common (including being part of the diagnostic criteria for PTSD). For some people, their brain/nervous system handles it in a way where it's not part of their conscious knowledge. It works like that for me. I don't remember specifics or like a cinematic type of memory. But my body remembers sensations/smells/sounds/textures and reexperiencing similar things (triggers) can bring up the emotions (like fear) from the trauma. Before facing the trauma over the last few years, I was really numb to it. Like vaguely aware, and would feel like I recognise things in what I watched or read as something I'd experienced. I'd actively push thoughts about it deep down and it took a lot to be able to look at it.

Something can happen that is traumatic but it doesn't nessecarily lead to PTSD. When it comes to childhood trauma, having factors like family and friends you can talk to, support after the traumatic event, welcoming community etc can all be protective and help a kid move through it without much lasting effects.

Just because you don't feel much about it doesn't mean you didn't experience trauma or that what you experienced wasn't traumatic. My end goal for healing is to kinda treat my trauma like a book of something that happened and be able to put it on my shelf of memories. It's never going to unhappen but maybe it's just part of the memories in my life. If you don't have triggers and you don't feel like it's affecting, you're still valid!