Can my floor hold a bookshelf?

Hi, sorry that I have no knowledge of construction. As showed in picture, my apartment floor seems has a little crack(or sink?) in the corner, not sure is this an issue or not? can I safely put a bookshelf on it?

Note: when I heavily press on the corner, the floor will sink a tiny bit.

https://preview.redd.it/74n1nsnhwfch1.jpg?width=4000&format=pjpg&auto=webp&s=d20b1de37c798d2bafb73b9c644a1df8aa18d47a