Let’s imagine a world where time machines are invented.
Hypothetically, what’s stopping anyone from travelling to the past, where the dollar is much more valuable, and buying things at a much lower price? What if you then go back to the present, sell those things at a higher price and repeat the cycle? And wtf would happen if everyone there started doing that?
So the easiest thing would be to buy cheap commodities that were expensive back then, go back in time and sell, then buy some kind of property or like shares in ibm. You could easily make a lot of money.
But you wouldn’t really be creating wealth, you would just be making it so you end up with it instead of someone else.
The best way to create wealth (assuming you can’t just create energy in the time travel process) is to take technology back.
Taking tech back (making a company with it so your rich too) would actually make humanity have a higher total wealth.
I personally would take solar cells and modern batteries back in time, might as well do some good with it.