That is a rufus error, just ignore it, they expect the new file signing but MSFT doesn't use it atm, just ignore it.
I mean... it's not really a Rufus error, it's more of a Rufus warning about something (currently) unresolved on the manufacturer side. But yes, ignore the warning, as long as you're getting genuine images or you yourself are performing modifications to ones and you know what's in them.
MSFT should use new file signing and rufus already expexts them to use it, MSFT doesn't use it, so rufus whines about it.
I wanted to be an... early bird this time and grab the iso from microsoft's servers before the url expires. I did it, I let it download until ~80%, but I had to stop it. And when trying to continue the download, with wget, I get that 403 error The direct link from buzzheavier does not seem to be "compatible" with wget though, so as to continue where it left, and I don't know what to do. Starting the download over is not an option.