Cropsensor camera VS Dx modus on Nikon z7ll

Hello everyone, I hope someone can help me with my question. Is the image qu ality noticeably less in DX mode (Nikon 7ll) or am I better off with a crop camera? I can buy a used Nikon prime 300mm f4D AF-S D for a very interesting price from a reliable source and I would like to combine it with the Nikon Z7ll which has IBIS, because the lens does not have VR and to have a range of 450mm in DX mode. I would then perhaps consider a telephoto lens later for even more range. Thanks in advance for your answer. Greetings, Danny