My impression (from briefly skimming papers about this a few years ago) was that there is clear evidence that myopia is strongly related to not spending enough time outside as a child, but it’s not clear to what extent the effect being outside has on eye development is from focusing the eyes far away vs. being in very bright surroundings.

I believe that someone did some studies involving outdoor schools or similar, that was considered to differentiate between those factors - being outdoors and reading was better than being indoors and reading.