I’ve never played any FromSoftware games or anything else in this genre but where would you recommend I start if I wanted to try it? I play on PC.
A lot of people got into From Software through Dark Souls 3 or Bloodborne, Bloodborne is PS4-exclusive, so Dark Souls 3 is usually probably considered the golden standard for PC/Xbox players. Until Elden Ring came, it was the most popular and the most well-known, I'd say. It's also in between, not as breakneck-hectic as Sekiro or Bloodborne and not as slow and methodical as Dark Souls 1, like I said, somewhere in between. (I'm now trying to be objective, I like other games more, but DS3 is generally very beloved among the general public).
There's another option - Elden Ring is really popular, because it is the first from game that got really
big and it can be really good for a newbie - there's, like, a million options to make the game easier or more fun for yourself, a million things to discover, if you get stuck, you can go around discovering million other things. Thousands of weapons you could try to combine, million types of potential playthroughs. As for the "money spent - content" ratio, there's nothing like ER - like Joseph Anderson has said - 'it's not "Dark Souls 4", it's "Dark Souls 4, 5 and 6", an AAA game that is being sold at full price and still feels like it's being sold on sale, underpriced'.
Dark Souls series (especially 1 and 3) is more about overcoming obstacles, Elden Ring (and DS 2 to a degree, but that may be just me talking) are more about discovery and sense of wonder (and general atmosphere of the place).
I personally started with Dark Souls 1 and it's still my favourite, along with Elden Ring, because it was the first and your first from software game you'll never forget. However, it is the slowest and the "clunkiest" game of them all, in a way that's also a plus (like I said, the combat is more methodical, slower) and the level design is amazing - everybody who finished the game could lead you anywhere in the world completely blind - but I don't know if you'd like it, too. In general, I'd say DS 3 or Elden Ring is the safer bet.
Sekiro is completely different, to a degree, it has an ingenious combat mechanic (you are dealing damage to health and posture, the two meters are interconnected, it's closest to an actual swordfight as you could ever get) and amazing atmosphere, but it's a rather separate thing altogether.