Came to make the same recommendation. It depends on what aspect of the games you find intimidating. Most people recommending Elden Ring will likely be assuming that you mean mechanical difficulty, but in my case, the openness, variety, stat numbers etc of ER are all intimidating.
Sekiro is more approachable in this regard, the way forward is mostly clear, and the mechanics are clearly communicated, so you’re just left with practicing them until you’re good enough to progress.
I’d say that most people who say Sekiro is one of the hardest fromsoft games probably came from playing souls or Elden Ring and have the extra challenge of unlearning some of the foundations. I hadn’t played any, and though Sekiro is hard as hell sometimes, it clicked with me pretty quickly. Completed 3 endings and most of the optional, hardest content so far
The first Headless I encountered in Sekiro. I was seeing enough progress and understanding what was being asked of me just enough to be stubborn as hell and kept trying to fight it head on, without having any knowledge yet of any helpful items that make the fight less rage-enducing.
Outside of Fromsoft, my NG+ encounter with the green swamp monster thing in Lies of P seemed SO much harder than the first time. So I’m not sure if this boss is considered easy or hard, but I didn’t consider it to be very hard going in for a second time and got quite stuck for a while…