My experience as someone who bounced off a couple souls games, playwd Sekiro, and then played Elden Ring:
Sekiro is not harder, and IMO most people who say it is come from a place of having gotten used to more traditional soulsborne combat. If you're struggling in Sekiro my main tips are to go somewhere else for a while, or just that you can straight up ignore most enemies in the game without consequences.
Sekiro is seen as harder than DS because you can't level up or change your build to overcome a challenge. But unlike DS, each encounter and level can be custom crafted knowing what the player is capable of.
Where the games don't differ is that the combat is fair and you'll get the same excitement and sense of accomplishment when you defeat a powerful enemy.