What OS version are you using? If High Sierra, there have been multiple posts where people couldn't get Safari to connect to Apple log in pages, iCloud, or sign into the page where you manage your Apple ID.
Safari can’t open a website. https://support.apple.com/guide/safari/if-you-cant-open-a-website-ibrw1071/mac
Safari – slow page loads. https://www.lifewire.com/safari-slow-page-loads-dns-prefetching-2259904
Safari - Unsupported third-party add-ons may cause Safari to unexpectedly quit or have performance issues.
https://support.apple.com/en-us/HT203353
Safari doesn't load a page or webpage items are missing. https://support.apple.com/en-us/HT204098
Are you running any anti - virus programs? Using a VPN?
Try setting up another admin user account in System Preferences/Users & Groups to see if the same problem continues. Please post back on whether or not this worked. Also try the Safe Mode. Please post back on whether or not this worked.
Isolating an issue by using another user account https://support.apple.com/en-us/HT204443
Safe Mode - About. https://support.apple.com/en-us/HT201262
If it works in the Safe Mode, try running this program when booted normally and then copy and paste the output in a reply. The program was created by Etresoft, a frequent contributor. Please use copy and paste as screen shots can be hard to read. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown. If the log won’t post, try posting it in Pastebin and provide a link in a reply. After pasting the report in a PasteBin page, go to the top of the page, and copy the address in the URL bar. Paste that in a new reply. Pastebin. https://pastebin.com/
Etrecheck – System Information. https://apps.apple.com/app/etrecheck/id1423715984?ls=1&mt=12
Web site version if required. https://etrecheck.com
