You mean an admin panel on a server application, right? At my current job, I'm on a platform team that supports hundreds of applications. Each of them have their own admin panels.
However, there are settings that apply to all of them in our library code. For those, we use feature flags, and they are loaded from a network service, environment variables, code and config files. The overriding logic is complicated for legacy reasons and prone to bugs, so we are moving to a centralized feature flag system.
Fair, that makes sense. Not a very common use case I think unless you're talking more about heavy use of microservices that need a feature flag across the entire suite.
However, there are settings that apply to all of them in our library code. For those, we use feature flags, and they are loaded from a network service, environment variables, code and config files. The overriding logic is complicated for legacy reasons and prone to bugs, so we are moving to a centralized feature flag system.