Most games these days, and indeed as far back as video games have existed, have promised players that they need no prior knowledge before diving in.
In the days before in-game tutorials, maybe you needed to read the manual, but that was it. Now, you don't even need to do that.
Even so, there are some games where the developer assumes you have at least some knowledge about the game world.
In general, this won't be a problem, but some games either won't make sense at all or will provide a more fulfilling experience if you've already played one or more other games in the series.
1. Metal Gear Solid
You can theoretically pick up and play a Metal Gear Solid game without playing any of the others. I know because I've done it. That said, if you do, you're not really getting everything you can from the game.
Before Metal Gear series creator Hideo Kojima was getting weird with celebrity friends and weird traversal mechanics in Death Stranding, he was getting weird with nukes and clones and, well, all the other weird stuff this series is about.
You need to play them all to get it, which is kind of my point here.
2. The Legend of Heroes
There are actually at least two different sub-series within the overall Legend of Heroes banner. You've got The Legend of Heroes: Trails in the Sky and The Legend of Heroes: Trails of Cold Steel. Both of these span several games.
Trails in the Sky looks and plays more like a PlayStation-era RPG like Grandia, while Trails of Cold Steel feels more modern, both in its gameplay and its look.
While you could pick up and play the first game in either series, you don't really want to pick either up on the second or third games.
3. Shenmue
Despite there only being three games in the series, Shenmue dates back to 1999. The latest entry, the aptly titled Shenmue 3 just came out in 2019.
While you might be tempted to jump in with the latest entry, you'll probably be a little lost. The Shenmue series tells its stories across multiple volumes much as much or movies do.
Even moreso than some of the other games on this list, this is an example where your best bet is to start with the first game, then move on to the second and third in that order.
4. Tales of Zesteria / Berseria
With the exception of numbered sequels, the Tales games are similar to series like Final Fantasy. While there are themes that stay similar from game to game, the overall story doesn't continue from entry to entry.
That differs with Tales of Zesteria and Tales of Berseria.
You can absolutely play either of these games without playing the other, or you could play them in either order. That said, because of the nature of the storytelling, playing Tales of Zesteria before Tales of Berseria makes the most sense as far as the games' lore is concerned.
5. Mortal Kombat (Sort Of)
I'm not saying you should go back to the original arcade version of Mortal Kombat or even the home console versions and play forward from there.
For starters, that's not necessary to understand the story in recent games. For another thing, there's a bad stretch after the first few games that's best avoided.
What I'm talking about is the mini-trilogy that started with 2011's Mortal Kombat. From here, the story flows through Mortal Kombat X and 2019's Mortal Kombat 11.
While you can get by without playing the other games, there are plenty of in-jokes and character moments that mean any fan of the series should just play through all three. It's not like the story mode is particularly long in any of them.