I recommend the new Sony A7III. I have already ordered one. It is a game-changer for its price/performance. Already the best selling camera (mirrorless or DSLR) at B&H Photo, Adorama, and Amazon.
https://www.sony.com/electronics/interchangeable-lens-cameras/ilce-7m3-body-kit

You can still find excellent compact full-frame Sony lenses like the 28mm f2, 50mm f1.8, 85mm f1.8, and several 35mm lenses that are not heavy at all. An excellent all-around lens is the Sony 24-105mm f4 . It is not heavy and balances just fine on the full-frame Sony A7-series cameras. I have one.

Yes the longer zooms like 70-200mm and 100-400mm are heavier, but every camera makers' full-frame 70-200mm and 100-400mm are heavy to have that many glass elements and image stabilization. Cheers

Fujifilm
Olympus
Panasonic
Sony

Read reviews online. Watch YouTube videos on the gear. Rent to try before you buy.

Each brand has a distinct market niche, so you have to decide what’s important to you.

GREAT lenses? All of them make some pro quality glass. Fujinon, Panasonic Leica, Olympus Pro, Sony Zeiss... plenty of choices now, with many more on the way.

Best JPEGs? Fujifilm.

Weight savings? Olympus or Panasonic.

Full frame? Sony.

Simple menus? Panasonic.

Great, classic ergonomics? Fujifilm and Panasonic.

Best video? Panasonic and Sony, but in different circumstances.

It goes on and on... Don’t try to make mrrorless into dSLR, or digital into film. Both are very different worlds, but it’s all photography.

I went from Canon and Nikon systems to Panasonic, because I make an even mix of stills and video, and I need to travel light. Your needs may vary.

The "kit lens" it comes with is excellent. I would not buy anything else until I got familiar with the camera and got it set up the way you want it. THEN decide what you need based on what you want to do with it. All the Fuji glass is excellent. The next one I would probably buy, based on what I like to do, is the 50-140 F/2.8, which is a behmoth of a lens, but according to Rockwell, "The Fuji XF 50-140mm OIS WR is the best APS-C telephoto zoom of any brand. It's optically superb, has fantastic image stabilization and is faster and better made than the others." But for general use, the 50-200 would be the other lens to have. Smaller, lighter and cheaper.
I actually do have the 50-200, and the 18-135, also a 12mm prime from Rokinon, as well as the kit lens.

I was just next to a guy trying out the Sony a9, 20 frames a second and you can put it in silent mode and not hear a thing. He was using the Sony 100-400 and he was getting some amazing shots of birds in flight, he was experimenting with different focusing modes, he was moving from a full frame Canon with a new the newer 200-400 and the 600 f4 Canon lenses. He felt the results were favorable.
I was shooting beside him with my Nikon D500 with the 200-500 Nikon lens and I felt their was no difference in the shots. But I am no expert, but, his outfit weighted less than mine by quite a bit. And, Sony is releasing a new 400 mm 2.8 for their e mount. But rumor is that it will cost an arm and a leg.
And, it seems to me that Sony introduces new camera's faster than any company out their. I feel like if I buy a body it will be 2 generations old within a year. Don't get me wrong, I believe Sony is moving very fast in the mirrorless market but my Nikon is still delivering great results and with the amount of Nikon lenses that I have in my stable I will continue to stay with Nikon for now. Sony has not wowed me enough to switch, FOR NOW.