Catalina 10.15.7 Internet problems

I installed the latest update for my 2012 MacBookPro yesterday. All worked fine afterwards, but today I have not been able to connect to the web, email or streaming apps. My wifi signal is good, my other devices can get online as usual, but every time I try to use Safari, Firefox or Chrome I get the message 'You are not connected to the Internet" (which I am). I have no firewalls or antivirus installed and have uninstalled my Malware app, but still no access to the web. What can I do??