I don't know why the backup was so big, but depending on what you have set to backup, a lot of files would have been downloaded and changed during the update.

I just got a new machine (Win10 Pro) with an NVMe M.2 SSD, and it actually defragged before my eyes (not trimmed) very early on in the loading process, so I am also curious as to what caused this to occur. IIRC, I had hit some "optimize" someplace that I have not run since. For whatever reason, that SSD did/does not register as an SSD, so I have been doing everything manually since. I am new enough to Win10 Pro that I do not know all of the inner workings of its guts, but am finding many things that need to be tweaked as I go.

toddbooster
I don't know why the backup was so big, but depending on what you have set to backup, a lot of files would have been downloaded and changed during the update.

The size was compared to the first post-update backup.  IOW:
 
- Windows updates itself
- Full backup is executed; 66G
- Next night incremental runs; 30G with no installs or updates in between.
 
Note that with my internet connection it would be close to impossible to download 30G in 24hrs.
 
Windows ran defrag on both SSDs.  This happened because auto optimize was re-enabled during the update process.  Even if you take SSD out of the discussion, Windows changed the optimize setting on it's own, so something to watch out for.