Is it not?? Something about distracting oncoming drivers is what I was told as a kid

In the UK at least, no: https://www.theaa.com/breakdown-cover/advice/driving-myths#light

It's not actually illegal as far as I'm aware, however it's not recommended: https://www.tomfowlerlaw.com/post/illegal-to-drive-with-interior-lights

Is it Illegal to Drive with Interior Lights On?

Generally, most states don’t have laws that explicitly say that it’s not legal to drive such vehicles with dome interior lights on.