Wolfenstein II is pretty tough on the hardest difficulty. The game doesn't let you run around much even on normal. It's really not that hard though as it just forces you to corner camp and lean mainly while doing some AI exploitation.
Nioh should be a decent challenge as the game has a much better combat system than Souls that requires mastery vs just being careful. Bloodborne doesn't really give you an "easy" playstyle like Souls but it's not really hard if you're any good at fighting games or combat action games.
Invisible Inc is a pretty tough game that's basically a stealth-based XCOM that's a roguelike. Another stealth tactics game is Shadow Tactics, which I have but haven't gotten far into it, basically tried the first couple missions (via the demo), loved it, bought it, but haven't gotten around to it yet. I read the later missions get really tough though.
It's pretty hard to find truly challenging single player games as you can usually exploit the AI or mechanics pretty easily. Most games' combat rarely have the complexity and depth to require mastery. The hardest difficulty usually only makes games less fun and just drags out the combat. For example, you can beat any monster on the hardest difficulty at level 1 just exploiting a certain game mechanic in Witcher 3, it'll just take you a long ass time to beat a high level creature, but it isn't hard. Any online competitive game is way harder than any single player game due to facing human opponents.
The best way to make single player games challenging is sorta impose your own rules on them like playing Dishonored like StealthGamerBR instead of just playing to beat the game, which isn't supposed to be hard as the games are about creativity not difficulty.
