Based on the downvotes my comment is getting it seems there's a lot of scientifically illiterate people on this site. So, I'll expand on what I said.

We cannot directly measure the one-way speed of light because doing so requires synchronizing two distant clocks without already knowing how fast light travels.

When scientists state that light travels at 299,792,458 meters per second, they are referring to the two-way speed of light (a round trip from a source to a mirror and back).

To find the speed in one direction, you need a clock at the start and a clock at the finish line. To sync those two clocks, you must send a signal between them but, any signal you use to sync the clocks travels at the speed of light, which creates a circular problem.