Can't access an old world due to it not loading after nether update - stuck on old loading screen

Hello! Today I just got the 1.16.0 update and tried to log onto a world I created before the update. The world wouldn't load at all. It also switched the background image from the nether update one to the bee update one.

 

Here's a video  (click on the blue text to see the video) showing the difference between loading a new world in comparison to trying to load the old one.