I try to play with the DAC+ ADC Pro, from the documentation, I need to install HiFiBerryOS. Is it true after I install the HiFiBerryOS, the RPi can't work as it did under the Raspberry Pi OS.
Yes, HiFiBerry is its own OS, so it needs to be installed fresh on an SD card, just like other operating system software (Volumio for instance). It looks as though dual booting isn't a possibility, either.
I believe it's fairly straightforward to use Raspberry Pi OS with HiFiBerry hardware, and HiFiBerry OS' github page clearly states what services are used for streaming functionality, so you could conceivably try and replicate that functionality within the RasPi OS if you absolutely needed the full OS functionality.
What documentation say that you need HiFiBerryOS? This is definitely a misunderstanding. HiFiBerryOS is our software that allows it to easily setup a streaming music player. However, our sound cards use the normal Raspberry Pi Linux kernel that it used in many distributions. Therefore, they can be used with many available distributions.
If you want to deploy your own software, we recommend Raspberry Pi OS Lite as this is the one that's easiest to configure in our experience.
Thanks for the advise. Yes, I am clearer now.