Here are some of my thoughts on the topic of Free Will as it applies to the possibility of Time Travel. Caveat - I am not a physicist, so while I’ve tried to approach and word this thoughtfully and carefully, it may be imperfect:
In regards to Free Will, that’s an issue that often stems from theories which suggest that we live in a universe where the future already exists/is pre-determined. In such a universe, the question of whether we can alter the outcome of a future event arises and subsequently often leads to concerns or issues with causality, such as potential causal loops/bootstrap paradoxes, etc. and, of course, “Free Will”.
In order to intentionally try to alter a future event, one must have access to knowledge of the future event and attempt to change the event from a point in the past. But if one is just traveling to the future for the sake of traveling and are unaware of, or not attempting to alter its course, it doesn’t really place any strain on arguments of Free Will. The traveler has simply chosen to move forward in time. They will make choices in the future they arrived at just as they’ve made choices in the past. Having no prior knowledge of the future point they arrived in or of any future point beyond their arrival doesn’t necessarily lead to any paradoxes, and from their perspective will appear as though they are still the one calling the shots, thus their sense of Free Will seems preserved - or at least not disproven.
It’s when you try to change an event that has happened or is going to happen through actions taken before the event, but are unable to change the outcome of the event is when questions about whether or not Free Will exists begin to arise.
*Maybe attempting to alter a future event from the past was implied in the original post, but it wasn’t quite clear to me. Apologies if this was the case.
As for the existence of travel to the future, we already know it’s possible and have for some time. At first theoretically and later proven, at least on small scales. As our propulsion tech advances and we are able to achieve greater speeds through space (especially if we are able to reach speeds closer to the Speed of Light), it will be more tangible and not just evidenced by specialized clocks in fractions of a second (like in the case of personnel aboard the ISS). Though I hesitate to call this kind of travel ‘Time Travel’ in the traditional sense, as it’s a one-way trip.