We noticed that these are the available train routes. Are we restricted to these tracks, or is it possible for us to travel by train to different cities on lines that are not connected to the yellow line?
The yellow line is a specific train line that runs between capital cities. However, there are many other train lines that run throughout Europe, and you can travel to many different cities on these lines.
This map is totally incomplete and confuses a lot of travellers. (I believe it should be removed but that's not the point here.)
There are a lot more railways where the pass is valid yes. The coverage works by companies and the vast majority are included.
Check https://www.seat61.com/interrail-and-eurail-reservations.htm
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