Where can I download Big Sur without using App Store?

I have a Macbook, Late 2013. Works fine, but I am unable to download Big Sur from the App Store. It keeps telling me that I am using the wrong password(I am not), or wants me to verify my identity using devices I no longer have.....

Can someone suggest a way to install/download Big Sur? I want to have a clean install using a USB key. Also: how can I verify that any torrents out there are valid? Apple seems to not be of any help....