So, Lenovo won’t let me update my BIOS on anything else than Windows 10 1703 Redstone 2 15063. And I can’t download that legally, I think. It almost looks like Lenovo is pushing me to torrent it or something. But before going full pirate on this, I thought I’ll ask here:
Is there a way to download that specific version of windows legally?
There is but I believe posting it to the forum still violates a rule of some sort.
Not sure how that is possible but PM me then.
Never used it and it’s not even an HTTPS site, but looks like they have what you need.
To my interpretation of the rules this post doesen’t violate any rules since ISOs can be downloaded from the internet without infringing any rules. Bypassing the licensing system it’s a violation.
I got a link to another website in the meantime. (Thanks @GigaBusterEXE) I believe your solution might work the same way.
It basically lets you download versions from microsofts server that aren’t listed on their website. So in the end you are sourcing directly from microsoft.
I don’t know if the website is doing more than that. It certainly looks the part. xD
So I’m not responsible and so on… 
But the download address itself is https and a legit microsoft server.
Yeah that page seems to have the right direct links. I used it several times back when the official 1803 update utility failed to run on a number of systems.
Sorry work and the weekend caught up with me. The website is: https://www.heidoc.net/joomla/technology-science/microsoft/67-microsoft-windows-and-office-iso-download-tool?start=4
The individual created a website and tool to download easily from Microsoft’s website. Again I apologize for such the delay from your response.