Decades ago, an airliner took off and flew two flights in opposite directions around the world. It carried two very accurate clocks. The clocks had been synchronized prior to take off to a third clock remaining stationary on the ground. When the plane landed back where it started a couple of days later, the clocks were out of sync by the amount predicted by relativity.

This was the Hafele-Keating experiment. More here:

https://bigthink.com/starts-with-a-bang/flying-proved-einstein-right/