After a long fight with building up a new iso with this version of Anaconda, I was able to boot up and select an ISO file on an NFS share as a source to install. Thank you.
I have tested this with the reproducer from the bug and it has worked well. I confirm it works.
I have installed this update and I do not see any problems so far.
The update works for me, however, this does not solve the bug #1640701. The button changed to Download, which makes sense, but then I still see no progress or activity and I do not know whether packages are being downloaded or gnome-software got stalled. @frantisekz told me he would see the progress bar under the Cancel button in adwaita dark theme. I did not see anything in standard gnome theme. This should be fixed to work for everyone.
This update solves the login problem, but it lets the gnome-initial-setup process run twice, which confirms what Adam has experienced, too. I will file a new bug for that behaviour.