It's because of neither clover nor opencore. It's because you installed it wrong~.
In Big Sir, you need to choose "pre-boot installation" when the Big Sir installer reboot the system first time. If you are using clover, you probably hide the pre-boot partition. So, you could not choose it. You chose "system disk-data installation" instead. It will install the OS but it will not work correctly. Two issues, (1) mac app store doesn't work (2) recovery partition doesn't work.
Clover User:
1. make the preboot partition show (remove "hide" in the config.plist).
2. install the OS again(it will overwrite only the OS. You don't loose your config/data), and choose "pre-boot installation".
3. after installation, choose "pre-boot partition to boot". You may think you are doing it wrong but it's the correct way in Bug Sir.
Opencore User:
1. opencore show only the preboot partition when installing the OS. So you don't have other choice. So, you are fine.
2. opencore show the preboot as normal after installation. So you don't acknowledge it boots with pre-boot. So, you are fine.