This problem happened to me too,
try decreasing the render distance or try uninstalling and reinstalling the client / minecraft
Sorry I didn't understand the stuff because I read quickly, anyway try to cancel the realm subscription (save the realm worlds) and try again, or check that it is compatible for realm
Sorry again and see you ❤️
Hi, I suggest you format your computer or try to free up some space on your PC, or try to see if the Data-Pack is compatible for your computer or your version.
From what I understand, it seems that Mojang has a problem with its servers, try again later, if the bug is still there contact Mojang again