I have a fairly old Honor7A phone and the store does not always open on it. I asked others about this, but everyone said that everything was fine with them.
If you tap to open the store and you're at least getting a loading screen, leave the device and see if it eventually loads. The store has a lot of stuff in it and it can take some time on older devices.
Something else you can try if you haven't already is adjust the resolution in the in-game options menu, that might help if load faster.