No, you don't have to play other games before XVI.

Most Final Fantasy entries are either independent of each other, or very loosely connected, even more so on the mainline. Only straight up sequels, prequels and spin offs would potentially require having played earlier titles.

Numbered final fantasy titles are not related to each other (e.g 6 has no relation to 7, which has no relation to 8)

A game is only related when it uses the same number

E.g Final Fantasy X-2 (ff10 2, not to be confused with 12, 12 revenant wings, FF7R, 13's two sequels)

I don’t know why people ask this about games all the time. I don’t think there’s more than a couple games (considering decades of games) where you need to play a previous one to enjoy the latest entry in a franchise.

Nope! All mainline Final Fantasy entries are independent! There's common themes, elements, character names, etc. but you can learn about them from any of the games. Final Fantasy XVI is actually pretty different in tone from the past several mainline games so it's arguably more distinct. That plus the active time lore system make it a great jumping in point in my opinion

As a general rule, unless it's a direct sequel like FFX-2, all Final Fantasy games are not related except for reoccuring enemies, bosses, and themes.

That's the best part of Final Fantasy, is that a lot of them don't really interact with eachother unless they are direct sequels and spinoffs (like Dirge of Cerberus for FF VII or FFX-2). At most, there is references and they all do share bits and pieces because they're relatively in a giant universe. Like, you're always going to see Chocobos. Bahamut is always going to be a part of the game in some role. Cid will always come around and vice versa.

But generally, the story will be different, the cast will be different, the mechanics will be different .etc

Not at all. In fact, this is probably one of the most standalone ones yet.

The only thing you'd get out of it by having played previous games is recognition of recurring names and enemies. All of the Eikons in 16 are recurring summons from earlier games. Enemies make appearances from other games (and a lot of them are just straight-up asset flips from 14). A couple characters like Cid and Mid are recurring names as well.

To be perfectly honest you'd probably get more out of having watched Game of Thrones than having played a prior FF game.

No, each story is self contained and in completely different worlds. The only things that carry over are some monsters and there's always a character named Cid