Could aliens detect Earth from old TV signals?

In principle, yes—but in practice, old TV signals are probably far too weak and messy for aliens to detect as “television” unless they had an enormous, extremely sensitive receiver and knew exactly where to look.

Earth’s early broadcast TV and radio signals have been leaking into space for roughly a century, so the oldest signals are now about 100 light-years away. That means only civilizations within that expanding bubble could have received them yet.

However, broadcast TV was not aimed at space. Most power spread out over Earth’s surface and then weakened rapidly with distance. By interstellar distances, the signal would be buried under noise and much harder to distinguish from natural radio emissions. Powerful, narrow, directed signals—such as radar transmissions—would be much easier to detect than ordinary TV broadcasts.

So the short answer: aliens nearby with advanced equipment might notice that Earth is radio-loud, but watching old episodes of human TV from across the galaxy is very unlikely.