Safari can’t open the page because the server unexpectedly dropped the connection. How do I open website now

"the server unexpectedly dropped the connection" can happen for a number of reasons, some of which may be beyond your control. Read If Safari won’t open a page or work as expected on your Mac – Apple Support for some suggestions that you may be able to implement.

Non-Apple "anti-virus", "cleaning", "firewalls", Internet "security" products including "banking security", various and sundry VPNs, proxy servers, are several examples of factors you can control. If you use them, don't. A lot of things won't work if you do.