Looking to up my Birding setup, what do YOU recommend?

So I'm looking to upgrade my Birding game and I'm lost in the rabbit hole. So instead I thought I'd ask the people who know the most directly!

I've been bouncing back and fourth between Full Frame and cropped (Sony A6700 / A7 IV) but can't quite decide which is better for me.

I'm based in the Netherlands, so typically low light scenarios. Ideally I'll pair it with something like a 200-600 lens.

Any advice is welcome. I'm not married to the Sony brand (I've also been looking at the Canon R7/R6 etc).

Cheers, Ze

(1) Budget, country, and currency:

• 1500 Eurs on the body (used with reasonable clicks is ok)

(2) What equipment, if any, you have now and why is it no longer meeting your needs?

• Very old D3300 - it's just very slow / unreliable in autofocusing.

(3) What kinds of subjects do you intend to shoot?

• Birds (both stationary and in flight)

(4) Is it primarily for photography, videography, or both?

• Typically photos but perhaps videos too? Not explored that.