First and foremost, no matter if you're using the most expensive and most technologically advanced gear in the world, if you don't know what you're doing, your photos will not be "professional quality." I've got a camera that initially cost more nearly $10,000, and a lot of my photos are junk...and I mean awful. Having the right gear will not necessarily mean that your photos will be awesome. You must understand this as it's critical in understanding what it actually takes to get "professional" photos.
At least 80% (if not more) of what it takes to make a professional-quality image happens outside of the camera. YOUR decisions as to what to photograph, where to photograph, when to photograph it (e.g. time of day, peek action, etc...) the lighting, your composition, your exposure settings, your choice of focal length, and your timing all tremendously important decisions. YOUR failure to make the right decision in any one of these points means that the image will fail in some way. Now with that said, having the right gear will help you achieve your end goal, but it will most definitely NOT be the reason behind you getting "professional quality" photographs. Snapshots are taken, photographs are made.
The answer really depends upon what type(s) of photography you want to do. For example, if you're a professional landscape photographer (or at least wanna be one) then you will want a high-end camera that has a lot of pixels such as the Pentax 645Z, Phase One, Hasselblad or the amazing 100MP Fufifilm GFX. These models are also highly desirable for anyone who needs to make ginormous prints.
However, these cameras are not designed for anyone who needs a very fast workflow such as photojournalists, sports shooters, and wildlife photographers. Yes, they can be used in these situations, but they're not ideal because of the relatively slow AF and shooting or frame rate.
If, on the other hand, you're into sports/wildlife, then an APS-C sensor camera would likely be the optimal choice. Why? Because of the crop factor, these cameras provide an extra focal length to your already very expensive lenses. An 800mm lens is going to cost more than $10,000. But a 400mm on an APS-C body with a 1.6x crop factor will set you back about $2,000. Add on a 1.4x teleconverter and you've got more than 800mm (equivalent to full frame format) for a whole lot less than the cost of an 800mm lens. That money that you save can/should be used to pay for your travel expenses to get to those amazing places where the great subjects are to be found.
A lot of photographers do more than one or even a few types of photography. For this reason, they need a camera that will allow them to get the various shots that they need, they way they want it, how they want it, and when they want it, too. This means that cameras like the Fujifilm GFX may not be a camera that meets this criteria for them. They may need a multi-purpose camera like a Nikon D850 or a Canon 5D Mark III/IV, or a Pentax K-1. Or maybe they're into sports/wildlife then the Canon 1DX or the Nikon D5, or maybe even some of the high-end mirrorless cameras like a Sony A9 or Nikon Z7 would be good enough.
As for lenses, most photographers, when shoot sports or wildlife, will go for a super-telephoto prime or zoom lens. But those same photographers, when shooting a portrait, will likely go for a 70-200 f/2.8 zoom or maybe even a prime lens like an 85mm or 135mm lens. It really depends upon their shooting style and the effect that they're going for. This, IMHO, is the hardest part. How do you know what you should be aiming for in terms of the look of the image? That's hard, and the answer is by shooting a lot and studying the work of the professionals in your specific photographic genre. It's just like if, say, you wanted to be a mast novelist in the genre of spy novels. Well, you have to read a lot of spy novels to understand what makes one good and an other great. You also need to understand the market, too. What's selling? I mean, this is how you put food on the table, right? If you've never read a spy novel, there's no way you'll ever be able to write a great spy novel.
Studying the works of the great photographers is crucial in understanding what makes a great photograph. It almost always (sports and wildlife being the exception to the rule) has nothing to do with gear, but what you do with it.
I once saw the work of Ansel Adams at a gallery and was amazed at the detail. So I went out to a camera swap (when camera swaps were a thing :) ) and bought myself an 8x10 large-format camera. was thrilled at the idea of getting shots just like Ansel Adams did. Well, um... long story short - I didn't. Even though I had the gear, I didn't have the technical and artistic talent to properly use the gear to get the shots that were even close to what Adams had done. Not because my gear was faulty, but because I didn't know what I was doing.
High-end bodies like the Leica, Hasselblad, Nikon D-what ever or the Canon 5D or 1D are going to be the professional's choice because of their ability to allow the photographer to consistently get the shot. The lenses that they choose will differ based upon what they're doing and their shooting style.