The latest version is 21H1
It took me days to update a relatives computer - and a friend just emailed me yesterday with the same problem!!!!!
Here is what I sent him
"Don't try to do it through Windows update - instead get the Windows Update Assistant.
Don't shut down and assume that it will start from where it left off - it won't!!! Put the computer to sleep if you have to.
Keep it plugged in - or else you will get "reverting changes" if the battery runs out!!!!!!!
Take a look at
https://www.windowslatest.com/2021/05/19/how-to-download-and-install-the-windows-10-may-2021-update/
I never got the "optional updates" option - but scroll down to
How to download and install the Windows 10 May 2021 Update using Update Assistant - try that option. It will download the update (and store it in a folder - if it fails search for a folder called MEDIA - you can save the download by copying that folder). As it downloads you'll get a progress % and it will then change to a preparing % - this is where it stuck at 99%:"
Good luck!