The boot.wim can take many minutes to load on some systems (depends on the BIOS USB 2/3 driver speed).
The download file is 'donationware' in that you must donate in order to be given a download URL, although if you Google enough, you can find a torrent link for a 5GB .rar download which can be unpacked to give a 10.8GB ISO file which supports UEFI64 and Legacy 64-bit booting.
I changed the filename to:
GandalfsWin10PEx64RS7-20H1_.isomap64.agfmisomap64.ISO
GandalfsWin10PEx64RS7-20H1_.isomap64.agfmisomap64.ISO
so that it would boot under E2B and agFM without prompting for options or showing a secondary menu.