Naturally, you have playlists for the Final Fantasy series, SaGa series, Mana series, NieR series and Chrono series. Other popular hits such as Bravely Default and Octopath Traveler are here too, with a number of aforementioned series’ including their remix / arrange albums. While there’s a lot of the library already included, there are some exclusions yet, some presumably due to how relatively new they are (e.g. Endwalker, FFXV).
People regularly upload ripped tracks of these game OSTs on Youtube anyway, so them being officially available is definitely a welcome treat without any concerns for copyright strikes. Other larger game companies have been taking the initiative as well, like The Pokemon Company uploading the Diamond and Pearl Sound Library, or the Tales series’ official BGM collection for work / study. Indie companies have officially uploaded their soundtracks too: Risk of Rain (Chris Christodoulou), Crypt of the Necrodancer (Danny Baranowsky), among others.
Outside of music, the Square Enix Music channel also has a talk with music director Keiji Kawamori, for the curious. The channel should be accordingly updated over time, so get started on your playlist of choice!