Hello @Yosefa0,
Generally, there's no magic shortcut you can set to allow guests to log in as there are too many different ways TVs provide the menu to select internet services and also so many different content services. Guests will just have to read the manual you leave to find out how to bring up the internet services menu. Then they can use their own acount details to connect to whatever service they've subscribed to.
If you use the TV make sure to log out after use. As part of guest changeover, you'll probably also have to check that each guest has logged out so you don't get complaints from guests that someone else has charged viewing to their account.
It'd be worth connecting to some service yourself just to make sure the instructions in the manual are correct and complete. That way you can note any additions or corrections in the copy you leave for guests.
I don't have a TV in the room I rent out so can't comment on whether guests would require that cable service be available.
In the "amenities" section there are boxes for both "TV" and "Cable TV". If no cable TV is available then signal this by not checking the "Cable TV" box. You could also say "internet TV, no cable TV" prominently in your listing description if you wish.
Steve.