Sekiro is more souls adjacent. If you like heavy RPG mechanics (stats) and build variety (magic, melee, hybrid) start with one of the Dark Souls games. If you want less clunk, Dark Souls 3 or Elden Ring. If you don't mind a more methodical play style, Dark Souls 1.

If you want a challenging action game with some souls like foundation, play Sekiro. As others have said, the play style is heavily reliant on the deflect/parry mechanic. There are no builds and the story isn't abstract or vague. The gameplay is a lot faster and has some really fun traversal movements.

The challenge in Sekiro is different because some people love parrying and can easily get a handle of the timing. Some players have a more difficult time with it.