Using Safari to access AOL email, clicking on an attachment (any of them), a red warning screen pops up. Using Firefox, on AOL, clicking on an email attachment but won't open. Have I been hacked? I tried to install Big Sur but got an error message.

Hey there BigSurInstallProblems,

Thanks for reaching out to Apple Support Communities. It sounds like you’re having a couple of issues with your accessing attachments from your AOL mail account from a browser and updating your Mac. We’d be happy to help.

Updating may lead to a resolution with the mail issue so getting that resolved may be a good starting point. What happens when you try to update? Are you getting an error? This article can help if so:

If an error occurred while updating or installing macOS

If the macOS Big Sur install file was downloaded, move that to Trash on your Mac and try updating again.

As for the AOL mail issue, does this happen if you access the account from other devices? That could isolate the issue for you. You may also want to try downloading the attachments using the steps here:

Download items from the web using Safari on Mac

Take care.