Cant open up worlds

I cant load into some worlds on 1.16.100. It would say: Unable to connect to world. please check your connection to the internet and try again. but the world files are on my own device on a windows 10, so why do I need an internet connection to join it? when I click on the world to join it, it would freeze at loading resources and then it would say it. I don't know whats going on but If It cant be fixed I will lose hours of work.