I believe this issue is only for 1.17.1. The issue is, rendering is not working properly. It's only allowing you to see what I think is about 25 x 25 chunks. If you go out of those chunks, three more chunks will load in but, only those three. After those three load in only some mobs and blocks will appear. I tested two worlds to see if it was lag because I commonly lag when just starting Minecraft.