Keep getting 'unable to connect to world' error message

I have checked my internet connection and firewall, and neither are the culprit. Other friends who use my realm are having the same issue. They use different providers.

I have had this game for several months, but have only been unable to play on it since Monday 26th January. I have not changed any settings on my computer, nor have my friends.

 

I'm running 1.16.201

Steps to reproduce:

1. Click on my realm (named Pandemonium)

2. The purple loading screen appears saying "Loading resource packs" and a 'cancel' button. I do not click this button.
3. Error message 1 appears saying "Unable to connect to world. Please check your internet connection and try again."
4. Error message 1 disappears and is replaced by error message 2: "Unable to connect to world."