I love my Huawei P20 Pro (except when I don't), but that's another topic.
I've made a little magnetic lens hood which had a huge impact on photos during sunny days and bright street lights in the evening sometimes.
If you want to improve it, use some black fabric on the borders (I used the gasket from a 35mm film roll canister).
You will need a 8x1mm magnet, but if you have a smaller or thicker magnet, it's not a problem, just glue it. I added 2 more magnets later on mine (as you see in the pictures) fot a stronger grip.
You will need a metal plate under your case! They go for less than a dollar on ebay (or your nearest mobile accessories shop).
Enjoy this proverbial holy creation from Rogue Filament :DramaticalMovieFadeOut: :fliesaway:
Add a little support for the magnet hole if you want, but you can ignore it and just do a little sandpaper magic afterwards.