no connection

Have you tried restarting/resetting the router?

Have you tried disabling all browser extensions?

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. Also try the Safe Mode. 

Isolating an issue by using another user account   

Safe Mode - About.       

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.    

Etrecheck – System Information.      

Web site version if required.  https://etrecheck.com

I am sorry you are having this problem. However, in order for anyone to help you, you need to help us by providing specific information as to exactly what is happening. What did you attempt to do? What was the response or message? When and how did this begin occurring? Did you change or install anything? Please click on the link below and read the information, then respond. Thank you.

Writing an Effective Apple Support Communities Question - Apple Community