I started with Fuji (popular choice here) because of the vintage look and dials which force you/ allow you to learn the basics of photography through twiddling knobs rather than going into menus.
However, I do a fair amount of low-light photography and ultimately the APS-C systems weren't offering the performance I wanted. I moved to Sony and have the A7C and am delighted with the quality. If you ever plan on doing some video too, Sony works great for both. Most other systems seem to specialise in one or the other.
Be aware lenses are far more expensive than cameras!
Look at what your proposed use-cases are when considering glass. Sony stuff is generally quite lightweight being mirrorless, which for me is perfect, it's similar size to Fuji but has the clout of Nikon.
With your budget don't bother with a kit lens. Go straight to a wide fixed aperture zoom lens and maybe a nice prime.
For £5k you'd get a Sony A7C / A7IV (£1500-2500) plus a Tamron 24-70 F2.8 G2 (£850) and a Sigma 85mm F1.4 DG DN Art (£1000) and some change, which would fulfil just about any need other than distance/ wildlife/ sports photography (you can always rent lenses for occasional use anyway), and those lenses are pretty much top-rated glass. If you wanted, you could easily add a microphone, gimbal, carrying solutions and more for a couple hundred extra. I've also added the Sony 24mm F1.4GM and Tamron 70-180 F2.8