It might be that you have play protect or some anti-virus system that prevents you from downloading any app that isn't directly from the app store or you have the "install unknown apps" option turned off on your device, if it still doesn't work after doing these you should try watching YouTube tutorials maybe one of them will help you out(or at least they helped me out)
ty for the help! after a few weeks, i downloaded it again it did Donwnload into apk but this happened again idk why, ( also i tried if other games like could download into my screen yk the ones that you need to download into apk first, it did so i tried gacha art but the same thing happened again ) 😭