1. Developer options are not intended for enabling "hidden features", it's intended for development and testing.
You have nothing to look for in there. The options in there are not necessarily functional.
2. Redmi Note 8 does not support LDAC. This excerpt is taken from Redmi Note 8's device features configuration file:
Code:
<!-- whether support LDAC -->
<bool name="support_ldac">false</bool>