Where are your Feature Flags resolved in your Client Side Rendered Web Application or React Native App?

This is more like a design question. We have an in-house AB testing tool and we want to understand what is the best practice on where the feature flag resolution happens in the code. By Resolve I mean where do we put the IF check like

if (feature.isEnabled) {
// show feature
} else { 
// show default 
}

If these happen at client side then for Native app or Single Page App we will need to deliver all the feature flags to the client devices (immaterial of the landing screen/page configs)

Please share some of your thoughts or design.