What lens to get for aviation/wildlife photography with a canon 2000d?

I'm busy looking to upgrade my lens from a Sigma 70-300mm DG macro to something with more zoom and sharper edges. I just don't know what to choose and what is even worth getting given I only have a Canon EOS 2000D/Rebel T7.

I'm looking for either a 100-400 mm or more. The Canon EF 100-400mm f/4.5-5.6 L IS USM II seems to be really good, but it's also pricey and I don't even know if it'd be worth getting it with the camera body I have.
While I don't have a strict budget, I'd prefer it if the lens is under or around 1000 euros.
I was looking at some sigma lenses too, but I'm not sure of the quality given the one I have now isn't all that great (though I'm aware it's a very budget lens). Are other sigma lenses like that too?

Is it otherwise maybe a better idea to upgrade my body and just get a cheaper lens for roughly the same budget? I haven't been doing this for all that long yet so i'm not sure what the better choice is.