To give a little more explanation on why direct injection is an issue - in the USA gasoline cars have EGR (exhaust gas recirculation) and crank case ventilation systems. So both some exhaust gas during certain operating conditions and the air from the engine internal open space is pulled back through the intake and run back into the engine. When that happens a lot of dirt and mostly oil mist from the engine internal air is then run across hot intake valves. As you would imagine that hot valves and oil and particles from exhaust gas bake their way onto the intake valves.
This hasn't historically been an issue because the fuel comes into the system upstream of the intake valves in every engine fuel system from carbureted to port injection. The gasoline has detergents in it that are designed just for this. They break up the oil and carbon buildup and clean the intake valves. So it's a non-issue. That is until you switch to direct injection. By moving the injectors into the cylinder head - you can spray high pressure fuel directly into the combustion chamber. That allows a lot of benefits. It can cool the cylinder air temps. It can shoot more precise fuel volumes. And it can shoot multiple sprays or vary the timing for different characteristics. BUT - since that fuel no longer flows over the intake valves, there's nothing going through to clean them. And the carbon builds up.
Toyota solved this a long time ago with its D4S system. It just used two injection systems. And when you start the car or run during certain operating conditions - it will inject the fuel in the intake runners or the intake plenum and the result is to clean the valves. That's why carbon buildup hasn't been an issue on Toyotas for a generation of vehicles. They figured out the problem and solved it. But there were some early ones that didn't work as well. I owned an IS250 and it only had direct injection and a single 7th injector in the intake that only ran on cold starts (you have to run rich initially to get enough fuel to the catalytic converter to begin the reaction properly). So in cold weather climates that engine didn't have issues - but in warm climates where it rarely needed to run the 7th injector, then there were carbon issues. I never had an issue and the Lexus dealer ruined the car at a service visit (long story - don't go to Larry Miller Lexus in Utah if you don't want someone there to strip your car for parts)- so I didn't own it out to higher mileage.
I think newer generations of direct injection engines from other manufacturers including Ford have finally mostly adopted the D4S design and added intake injection. The newer EB engines I'm pretty sure have done this. I'd guess the only DI engines you'll find anymore without dual injection systems are the very cheap economy cars that aren't expected to last a long time.
The 4Runner engine is so old that it doesn't even use direct injection. It still only runs port injection. It's basically a 90's engine design and doesn't have the problems associated with direct injection. Intake carbon buildup should never be a problem. All fuel sold in the USA at gas stations should have detergent in it that is good enough to clean the intake valves.
Edit:
Here's a good picture that helps show where the two injectors for each cylinder live in a d4S system. In the 1GR that is in the 4Runner - only the upper injector exists. The valve you see on the left that is open - that's the intake valve. And the carbon buildup problem happens on the top of that valve and around where it seats. Eventually enough carbon and oil gunk can build up there if not cleaned that it won't seal anymore when it closes. And then you lose compression and have lots of engine problems. But you can see in the picture that the upper set of injectors (orange spray) will send fuel with detergent through to clean it. The lower (direct injector) alone would not work to clean it.
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