Leaving this for other people that may be looking for the answer. it’s fairly easy to do in C++.
FNavigationConfig struct in the Slate application controls which keys are responsible for UI navigation.
To simply turn off tab navigation, follow the code below.
#include "Framework/Application/NavigationConfig.h"
#include "MyGameStateBase.h"
void AMyGameStateBase::BeginPlay()
{
Super::BeginPlay();
FSlateApplication::Get().GetNavigationConfig()->bTabNavigation = false;
}
You may also make Your own NavigationConfig by subclassing FNavigationConfig, if You want more control (like dynamically turning the nav on/off)