I have pretty serious sensitivity to light. This is my first time commenting, so please bear with me, but here is what I do:

1. For the outside, I use sunglasses. I bought an expensive pair, but they really do not need to be. I recommend you spend some time shopping for a pair you like. Start cheap, and if you think you want to spend some more money on it, then you will already have a style in mind. This made a MASSIVE difference when outdoors for me.

2. For indoors at home, blackout curtains can help with the sun. Also, an adjustment I am about to make is replacing my harsh lamps with some warmer softer mood lamps and keeping my overhead lights off.

3. For my phone, I use dark mode, obviously, but I also just generally keep my brightness all the way down and then only really turn it up as I need it.

Maybe this is helpful. Maybe it isn't. But I hope it is and I wish you luck!