I Cant able to install an Xposed Installer APK that I got from a dodgy spam site In My redmi y1 its current android version is android 7
Don't install APK files you get from spam sites like the one you originally linked. They probably contain malware. Instead, go to the official thread on XDA and follow the install instructions there.
Note that you can't install Xposed just from an APK. You need to flash the Xposed framework to the system first, which entails unlocking the bootloader. The official APK file is just a tool for managing the different modules that Xposed uses.