It's a third person action game with a focus on melee combat, so that's similar. The combat in Nioh is more sophisticated, with different stances and a Ki (combat stamina) management system.

Nioh has a focus on skills (combat skills and also magic and ninjitsu complimentary skills) and consumable items, and not just a light and heavy attack.

Nioh, at it's heart, is an RNG loot game, with a heavy focus on equipment and character builds, think ARPG with infinitely better combat than something like Diablo.

I played and enjoyed DS 1 & 3, I prefer Nioh, I find the combat to be much more satisfying.

I see you already own Nioh, so you have nothing to lose by trying it. The early game is quite tough.

They're very different, but they do share some similarities.

Nioh is fantastic, and so is Dark Souls 3, do yourself a favor and play both. ;)

• (Both) Nioh story are serviceable, sometimes meh.
  
• Compared to Souls games, lots of fundamental mechanics are quite similar (Bonfire vs Shrine, leveling with Souls vs Amrita, etc).
  
• Exploration is okay, but overall level design wasn’t at souls ballpark. Where Souls level design are interconnected, Nioh levels are mission based. You can choose what mission you wanna play (or replay).
  
• Itemization is significantly different. All items in Souls are fixed. Some weapons/armors random dropped from enemies, but when it drops it’s exactly the particular item. Nioh’s loot is diablo-esque tiered items/armors/accessories rng drops. You can forge countless times, or farm endlessly just to get the best items for your build and play styles.
  
• Thus build variety in Nioh significantly abundant, and can be overwhelming.
  
• Combat is what Nioh really shines. Fast paced, somewhat between Souls and Sekiro. Learning curve is quite steep. But once you get the hang of it, it’s the most satisfying third person action rpg combat. Almost feels like hack and slash, but you must also manage your Ki (similar to stamina in souls games) with rhythm in fights.
  
• If you enjoy Souls games epic boss fights, you’ll probably like Nioh boss duel even more.

EDIT:
each Dark Souls games (1, 2, 3 includes Elden Ring) are different games. Which every sequels mostly expands playing experience from its predecessor.