I've just downloaded and installed the 2020 R1 package, but I had some identical issues as described in the link you provided.
My download folder is not on my main partition (because it's a ssd, and I don't want to constantly write on my SSD, which would both take a lot of useless space and damage the disk). So I moved the extracted folder to C:Documents and then ran the setup. It solved the problem.
Hope this could work for both of you