What's the best way to store world objects placed by the player? (Like Animal Crossing or Stardew Valley).

I want to create a topdown, 2d city builder game, but I'm not sure how to efficiently store/save objects placed by the player.

I was thinking about creating a scriptable object with a dictionary of gamebject data. But this could reach thousands of items.

Then I thought I could create a scriptable object (or SQL DB) containing a hastable. Using coordinates as the key (and object data as the value). I was thinking this might be effective since I can quickly and easily load objects in range of the player, and destroy those that aren't.

Maybe there's a better way?