I need a new input device for my Elegato TV app

Elgato dropped the EyeTV product many years ago. You may need to buy a replacement via ebay or similar. Make sure it supports your region's TV format. Other (non-Elgato) TV tuners for the Mac may also work.

Note that EyeTV app is a 32 bit app and so will not run on OS more recent than Mojave.

Have you looked at Elgato's website?

Have you tried contacting them directly to inquire about support on the issue?

Can you elaborate?