I think time travel as a being who perceives one dimensional time linearly is not possible. And for any entity who doesn’t perceive time linearly it would be no different from traveling in a spacial dimension. It’s just travel. Anything that entity does in that point is a permanent fixture to the entities that perceive it linearly.

So yes, if someone could travel in time in the SciFi sense, they wouldn’t be able to change anything in their past experience (direct experience or prior to their perception, but in their event line) because that’s already part of that point in spacetime to anyone who experiences it linearly.

But also, it’s likely that time is not one-dimensional just like we know space is not only three-dimensional. So it is possible that you could end up in a separate “branch” of time that your past self from your perspective will never experience (directly or as past events), because it’s not the same point in spacetime as the event in your direct past timeline. But it’s not like there is a specific set of “branches”. They likely don’t branch off from a single trunk into the other dimension(s) or if they did “branch”, it was at the same time as all other “branches”, the beginning of the universe, not as specific events occur like in SciFi. And the changes you make in those branches were always part of those branches to people who will perceive the future of that timeline.