I think that I MAY have discovered why at least some people are having problems downloading the sim.
Last night, I made my fifth attempt at downloading it - the previous ones had either stopped part way through, or completed, but took a LONG time and used a LOT of data. I have a 50Mhz connection, and on previous efforts it was taking me more than 24 hours to download it, then I couldn't "download" all of the packages.
Last evening, I downloaded it in just under 9 hours, and the data hit on my ISP was just on 210GB, which compares to 950GB, which my last attempt consumed over two and a half days, and failed repeatedly to load 17 plus updates from WU 1, 2 and 3.
Today, I've just completed updating all the packages, and they are all there.
What is different?
Well, I've done two things differently - one I don't think would have much impact on the download, and one that almost certainly did.
The "low impact" was to switch from the 512GB SSD PCIe NVMe that came with the laptop I'm using, to using an after market 2 TB SSD.
The other, and I think that this is probably the key to why it worked this time, was I used a VPN into my closest city.
I have no idea WHY it worked, and I can't say that it will work for any one, but for those of you who are still struggling to download the sim, I reckon that this is certainly worth a try!
My VPN is SurfShark, BTW, but I don't think that the actual VPN you use is likely to make much difference.
Good luck all, and please let me know if you try this, and if you do, did it work for you.