Recently unable to load websites

After installing AVG Free on Mac OS10.11 (can not go higher)…  & then uninstalling AVG SOFTWARE (as far as I can see), I am finding various searches on Chrome & Safari, state that Website is not secure.   Even some I have used for years…
Is there any connection between recent installation of AVG & this block to my access?
Besides looking in Applications, could there be some remnant of AVG left on system causing this problem?
I have done a Malware search.
Many thanks

Hello Pip,

We are glad to look into this and help you.
Are you using any other AVG programs on your Mac OS?
If possible, could you please share us the screenshot of message saying that website is not secure in order to understand better and resolve it?
For taking a screenshot, please refer to this article: https://bit.ly/3lO7bwi 
Please confirm whether any other Antivirus program is installed on your Mac.
Thank you and please keep us informed.