OpenGameArt has a section for music[0], itch.io also has a bunch of free music assets[1], but do check the license before using them. I use these often and there's some surprisingly great tracks there.

[0]: https://opengameart.org/art-search-advanced?field_art_type_t...

[1]: https://itch.io/game-assets/top-rated/free/tag-music

I’ve used music from Kevin MacLeod [0] and Heatly Bros [1] in projects.

[0] https://incompetech.com/music/royalty-free/music.html

[1] https://heatleybros.bandcamp.com/music

https://luckylionstudios.com has a ton of royalty-free music, it’s not free, but it’s cheap enough it basically is.