Games are all near direct sequels (2 literally opens at the end cutscene of 1) with a whole lot of lore and story built up between them that will make absolutely no sense without the context of the previous games.
I see this a lot, but Falcom puts in a lot of work knowing that this may be someone's fist Trails. While ideally some background in the series helps, the games typically include all the information in some capacity to catch someone up on the general story. I started with ToCSII on PC and was able to catch up pretty quick. Obviously going back and later playing ToCSI later filled in gaps and made me appreciate some story beats more, but it wasn't like it was impossible to follow.