How to fix the 'Safari Can't Find Server' Error?

This is more likely a network issue than a Safari one.

When you enter a URL in Safari, a few things happen:

First, Safari tries to resolve the hostname (e.g. 'discussions.apple.com' to find the IP address of the server).

If that succeeds, Safari tries to open a connection to that IP address on either port 80 (HTTP) or 443 (HTTPS).

If that succeeds, Safari sends a request for the page (e.g. 'GET /thread/255672437'

Any of these things could fail.

For step 1 - DNS, the DNS server may fail to resolve the address, or the address may be invalid (e.g. not a valid server name), or there may be some configuration on the DNS server that is specifically blocking the request (for example, some DNS servers support blocking certain domains or hostnames because they're known to host inappropriate material, malware, or other malicious content.

Any of these failures would result in a 'cannot find server' response.

For step 2, assuming the DNS resolves, Safari tries to open a connection to the IP address.

This could fail because the IP address may be invalid, or the server is offline/overloaded.

It could also fail because your system, or some other device on your network, is configured to block access to that IP address (for similar reasons as to why the DNS server may not respond).

Many ISP routers implement filtering at this level to block known malicious sites.

Failures at this level would generally result in an 'unable to contact server' error message.

Assuming you connect to the server, the request can still fail - the request may be invalid, the server may be too slo to respond before the connection times out, or your router/firewall or other device on your network is restricting access.

All of these are outside of Safari's control.

In order to debug further you'll need to provide more information.

For example, what specific sites does this happen on? clearly not all, or you wouldn't have been able to post here.

Can other people access the site? other people inside your local network? or remote? this may highlight whether the problem is on your network.

Can you access the site from a different location? Again, this may highlight something on your local network that's blocking the site(s) in question.

Are you on a VPN? Using a VPN changing your network routing and it may be something on the VPN server side that's blocking the connection.

In summary, there are many ways this could fail. It will take some triage to work out which specific causes are in effect here.