Mid 2011 iMac factory reset issue

I recently obtained a mid 2011 iMac that was running on Sierra 10.12.6. I was advised to do a factory reset for security reasons etc. Everything went well until reinstalling from the recovery hd. At the end of that install I kept getting an error I tried the process for factory reset a number of times and eventually I ended up with Mountain Lion 10.8.5 installed. It stated there were updates. It attempted to take me to the App Store but it stated I wasn’t connected to the internet even though I was and able to connect to other Webb pages. I have tried accessing Apple.com but I still get the message stating I’m not connected to the internet!.I’m not a stupid person but I do have cognitive issues as a result of a severe brain haemorrhage 10 years ago following which I changed all my tech to Apple as I found the software more intuitive but this has me stumped.