There is currently a fix for customers who are able to access the Solr Apache API admin page from a workstation. Download EM version 21.12.2 and install it.
If you are still able to access the Solr Apache API admin page on a workstation that is not the local NVR hitting port 8983, it is because they have turned off the Windows Firewall.
They will need to block access to port 8983 in whatever firewall software they are using.