Steps to reproduce the issue

Easiest way is to have a local site and disconnect from the internet. Confirm that your site cannot see updated by checking for updates using the joomla update component

Expected result

In J3 the checks for new joomla and extensions will display an error on the control panel bottom left
In J4 the checks for new joomla and extensions will display an error on the control panel icons
In J4 the ajax checks for new joomla and extensions will display an error on the system dashboard

Actual result

No errors and everything reported as upto date. I noticed this on a client site where the sysadmin had firewalled the server to prevent external checks. As a result they didnt know they were multiple versions out of date

Additional comments

Some sort of icon/text (depending on the location) to show a warning that the site couldnt check would be the minimum expected.
Definitely is wrong to show as upto date

This really should be fixed in J3 and J4 but will probably need separate PR as the code is different for this