If you are running Joomla 4, and doing the Joomla 5 Pre-Update check and receive this error "An error has occurred while fetching the JSON data: HTTP 500 status code."
Try going to System - Update - Update Sites and have a look at your list of components - you probably have a lot of out of date components listed, they will show as grey X. Click on the "Rebuild" button to refresh the list.
After rebuilding the list all of the items marked with greyed out X will have disappeared
Now go back to the Joomla Pre-Check and it should complete normally, without the 500 error. Yay!
