safari can't connect to the server.

Go step by step and test.

1. Restart the router.

2. Deselect Proxies, if selected.

   System Preference > Network > Advanced  > Proxies Tab

   Unlock the lock if you have to.

   Under "Select  a protocol…”, uncheck any box if check-marked.

   Click "OK” then  "Apply”.

    https://support.apple.com/guide/safari/if-you-cant-open-a-website-ibrw1071/mac

3. Uninstall any Profile you have not installed knowingly.

    Section: Remove a configuration profile from your Mac

    Profiles: https://support.apple.com/guide/mac-help/configuration-profiles-standardize-settings-mh35561/mac

4. Disable/uninstall any anti-virus software or web monitoring software if installed.

5. Disable VPN and test, if installed.