I am kind of big nostalgic person, so music from the first decade of 2000's is what suits better for me. Usually I like to use Youtube when playing, and I will recommend it for the sake of simplicity and zero costs (but of course, you can use any music streaming service as well to execute playlists ). However, I usually have a big variety of preferences for music. I am citing this specifically because many old and classic Tibia videos got music like this on the first decade of this millenium, not to mention that it was the style most preferred from many players from this era, so it brings memories!
This one got plenty of huge hits from this time. It depends really about the music or my mood if I skip or not some of them:
However, if you enjoy for example "classic rock", you can simply use the search mechanism on youtube and find the better one for you! Make sure to check "playlist" on the filter's search. On the example below, you can see playlist options themed as "classic rock"