Cosmodial Sky Atlas

An well established alternative to compare against would be Stellarium mobile version. Stellarium mobile version is an app, not a web page and the best way to get it is indeed through play/app store. I don't think any of those are bad things.

There is a web version of Stellarium too.

https://stellarium-web.org/

OP has red light mode in the hamburger menu click the moon icon under sky.

But if you didn't know..

Have an iPhone (I am sure android has this but I am not familiar) and want to play with this outside at night?

Go into accessibility and turn on color filters to make your screen red and if you are in a very dark place and your eyes have adjusted turn on the white point adjustment and dim it down as well.

Both can be set as shortcuts to your side button triple click or configured as shortcuts to pin to your Home Screen.

All that said, OP a high contrast mode would be sweet.

Took a second to find the smartphone mode but I'm impressed.