Recently I've been spending a lot of time on this hardcore world I made. By accident I went on 1.17 even though I started on 1.16.5

It gave me the option to change back and I did so after seeing the warning of the game might crash. Everything worked when I spawned and it was like I never left. That is except for the fact that mobs of any kind wouldn't spawn. I went to creative through the Lan feature and turned on mob spawning but it still doesn't work. There's just barren wasteland after barren wasteland. Every villager every mob (except for squids for some reason). I myself placed down a couple mobs to make myself feel like everything was back to normal, but it feels like I've cheated and that ruins the point of hardcore. I've spent 11 hours on this world and I haven't even died. If there's a way to fix this please let me know. I sent a picture of how empty the world is in a plains biome.