The answer to this question is a bit complicated. In short, yes, TV and internet can use the same cable, but there are some important caveats to keep in mind.
First, it's important to understand that there are two different types of cables that can be used for TV and internet: coaxial cables and Ethernet cables. Coaxial cables are the most common type of cable used for both TV and internet service. They're typically thicker than Ethernet cables and have a copper core surrounded by insulation and a metal shielding.
Ethernet cables are thinner than coaxial cables and have eight wires inside them (coaxial cables only have one). Ethernet is generally faster than coaxial, but it's also more expensive. So, if you're looking to save money, using a coaxial cable for both TV and internet is perfectly fine.
Now, when it comes to actually connecting your TV and internet modem/router, there are a few different ways to do it. The most common way is to use a splitter. A splitter takes one incoming signal (from your modem/router) and splits it into two outgoing signals (one for your TV, one for your internet). This is the simplest way to connect both devices using the same cable.
Another option is to use a MOCA adapter (or MoCA bridge). This device converts the signal from your modem/router from Ethernet into coaxial so that it can be used by your TV. This is a great option if you want to use an existing coaxial cable setup but don't want to buy a new splitter. Keep in mind though that not all modems/routers are compatible with MOCA adapters - you'll need to check with yours before purchasing one.
So, in summary: yes, you can use the same cable for both TV and internet service as long as it's a coaxial cable ƒand you're using either a splitter or MOCA adapter (depending on compatibility).