when I switch to 10x telephoto lens my image becomes Granny

I bought a second hand as 21 Ultra and I saw every camera has small dust particles online birthday image qualities clear but when I zoom more and switches to 10x telephoto lens the image becomes grainy and little bit blurry when I zoom in to take some photos of trees the leaves become kind of double is this problem fixable just needs cleaning servicing 🤷🏻