The downloaded ubuntu 20.04 can't be found by Rufus

Thank you Jim!
Just found the email and rushed to thank you.
I think I remember some md4 at the end of the downloaded file - not sure. Deleted now, of course.
I will go in detail over the material you gave me.
The Windows 10 was pre-installed on the laptop by the manufacturer.
The previous downloads were done directly, not torrent.
Have a great weekend!

I used one of my kids's laptop which runs Windows 10. With Firefox on windows 10 the ISO's download fine, see them in the Downloads folder and i can open them with Rufus.
I'm writing the iso to usb stick with Rufus this very moment.

I think we're dealing with a PEBCAK here.

I actually think Luft's Windows PC has other problems, maybe some kind of virus or malware or maybe a Windows problem with the registry. Which is why I recommended he try a friend or relatives PC or buy a preloaded USB. MS is certainly not blocking people, they would be up on antitrust charges again if they did.

Thank you, Maik. So, it's my machine.

The weird thing is that none of the downloads I executed used Firefox, yet Firefox icon appeared each time on the downloaded file!
I always used Brave!
After I uninstalled Firefox and repeated the downloading - each time with Brave - the files appeared each time with no icon!
Have you thought about the AI Singularity?
If it takes control, no more internet for the masses!
Is there any way to make queries to the makers of Linux, Ubuntu about an alternate internet?
Naturally, servers would be needed.
By the way, the WEF had a meeting on the "cyber pandemic".

"Social credit" scheme of China is supposed to be implemented all over.
One's obedient behavior will "mine" cryptocurrencies. Otherwise - starvation.
How will we organize if the internet is shut for all dissidence?

Anyway, I thought this is of concern to all.

I don't think it has anything to do with the computer being infected. On the other hand if so then his anti virus should have given a warning already and it's easy to reset or reinstall Windows 10. It makes no sense to continue with the discussion as there are many other solutions luft could try first.
As you said try it on a family member or friend's computer. Or as i suggested, reinstall Windows 10 on his machine.