Mirrorless Camera (Deepings PE6)

I know this is a very big ask: my current set up is a D7500 coupled with Sigma 150-600 contemporary. I handhold & shoot mainly birds. I need a lighter set up because I have been diagnosed with a spine condition. I’d ideally like a Nikon Z6 2. I know this is a very big ask, but if I could get the camera free, I will be able to afford a much lighter prime lense. Even used prices are too high for both at the moment. I like cameras with programmable custom settings, because I am neurodiverse. Being able to pre programme for in flight & still makes photography more accessible for me & all my other lenses are Nikon, so I wouldn’t have to replace everything.