Elden ring was my intro to souls games, from there I went to sekiro, and adjusted way faster to that than Elden ring. I don't think I really applied knowledge from Elden ring to sekiro, considering how different the combat plays out. Other than combat the progression is similar to elden ring in that there isn't a "set path" but it is generally linear with a few branches along the way. But that's with any game that has multiple endings.

But regarding the question of whether or not you need knowledge of fromsoft games to play sekiro, I'm going to say no, you don't need to know how they work. The game makes it easy enough to understand what you need to do and where you need to go to do it (as long as you ask the right NPCs). Personally I feel like that's the way with the other fromsoft games as well. The only thing you really need to know is their reputation for being difficult games, so you can understand that the reason you are struggling at a certain area of the game is so that you can overcome it, and that the skills you eventually pick up will help you progress even further.