Time travel to Earth’s past would be cool to study history. But how to not accidentally ruin our timeline?

I think the real progress is to be made in space. Send a probe to a solar system 50 LY away but back in time to arrive the same day you sent it. It can travel really slow too, because time isn’t a concern.

If there is a habitable planet, send settlers there at the earliest time in history possible. Settlers can be robots that just build infrastructure and plant stuff for 10k years. Then go yourself.