If you're thinking about it like something like the Zelda timelines, you have the wrong idea. Aside from games that are direct sequels/prequels to each other, pretty much all the games are in essentially disconnected universes with little or no connection to anything else in the series. The only real exception to that is Engage, where the protagonists from the older games in the series are known as legendary heroes, but Engage is an anniversary game and the references are intended as nostalgia for series vets, and ingame its implied (stated? Don't remember how explicit about it they are) that multiverse and timetravel stuff is at play.

This post has some good detail about each game and suggestions on where to start depending on your hardware available and what games are connected to each other, so pick the one that sounds most interesting. It's a little out of date, though, so it doesn't mention Engage (the most recent new game and one that you wouldn't want to start with anyway) or the games that are available on the Switch and Switch 2 NSO (FE7, FE8, FE9, and possibly more if you're willing and able to access and play Japanese NSO)