So many websites are being run (especially by the government) that were designed years ago to be compatible with Internet Explorer. The web designers did not bother to update them and make them compatible for the newer web technologies. Such websites work smoothly with with Internet Explorer but not with any other web browser.
For opening such websites, you can either use the actual Internet Explorer that still exists in Windows 10 (you have to launch iexplore.exe for launching Internet Explorer), you can run older versions of Windows in VirtualBox, or you can use the Internet Explorer Mode in the new Microsoft Edge browser.
The new Internet Explorer mode in Microsoft Edge browser opens the websites inside the Edge browser but using the old Internet Explorer rendering engine. Inside this mode even the old ActiveX controls can be run, making it fully compatible with very old webpages.
In order to load any website in the Internet Explorer mode, you have to first open that website in the Edge browser, then click on the menu icon (three dots near the top-right corner of the Edge window) and select More Tools → Reload in Internet Explorer Mode from the menu.
When that website is reloaded in the Internet Explorer mode, you will see it shows an Internet Explorer icon in the address bar. You can click on this icon and it will display that “This page is open in Internet Explorer mode”.
After you have used that website in the Internet Explorer mode for a while and now you want to get out of the Internet Explorer mode and go back to the new Edge web browser, you can select More Tools → Exit the Internet Explorer Mode from the menu.
This way you do not have to exit Edge web browser for accessing older websites that are designed to be used through the Microsoft Internet Explorer browser.