I would suggest you update to 1903 instead of 1909. It is somewhat more stable and has fewer problems.

But if you want to continue to try for 1909, I suggest trying this:
+ Be sure you have no third-party WU blockers running.
+ Turn off quick startup
+ Be sure metered connections are turned OFF.

In an elevated command prompt (cmd.exe – Run as Administrator)
+ chkdsk /f   It will ask you to reboot, agree and reboot
After the reboot and the computer finishes the boot process, in an elevated command prompt
+ DISM /online /cleanup-image /revertpendingactions
+ DISM /online /cleanup-imave /restorehealth
+ sfc /scannow
+ Run the Windows Update Troubleshooter in the Settings app under Update & Security.

Record any errors any of those report.
If there are no errors, try updating again. Be patient.
If it doesn’t work, come back for other possibilities.

Highly recommend you turn off all protection in MBAM until the update is complete then re-enable.

If you are moving to a newer version of Windows 10 (e.g. 1809 to 1909), I think you would have more success by downloading the 1909 ISO file and running it directly in Windows.

Once into the 1909 ISO setup screen, you will need to make a couple of choices:
* It will ask you if you want to check for updates; tell it NO. (You can check for updates later; doing it now will slow everything down.)
* You will be asked if you want to keep apps and data, keep your data, or keep nothing. Tell it to keep your apps and data. Keeping your apps and data means that only Windows will be changed; your programs and data will remain unchanged.

Pursue ISO as desired ….. but in my first Win 10 Ver Upgrade my “Stuck on 91%” install was remedied by DIS-abling, not Uninstalling as some did, my ESET, Mbam, and SuperAS security Apps. Worth a try, and I had several Macrium Images made B4 I started all of the Upgrade. I Have NOT Disabled Security Apps since, but that time it was required.

I have had an issue today also – my computer had asked me to do the install update for a few days and I did a remind later thing – because I know how long updates can take – so today my computer decided to just go for it – and then got stuck on 91% for about 4 hours – I decided I had to interrupt  it and since then have this creepy blue screen which I think from reading up is a BIOS thing – but it won’t let me negotiate any keys – I can tab from Boot Manager to Advanced but no arrows work and despite several attempts at hard rebooting no luck.  I just want to get past what is on my screen to actually resolve it – and it won’t let me go anywhere except possible to the hospital… any help most certainly accepted.

I just need to get the boot screen away so I can actually access the computer to sort any suggested options re update – just can’t get rid of it and it won’t let me go anywhere

I think antivirus can be blocking update. But thats just wild guess. I definately would like to see windows log and find, what EnevtID was going on..