Hi,
Thanks for your bug report. The error you’re hitting is here:
jan 07 21:11:55 endless eos-updater[1016]: Error occurred whilst pulling flatpak flathub:runtime/org.freedesktop.Platform.openh264/x86_64/19.08: While trying to apply extra data: apply_extra script failed, exit status 256
It’s a known issue and a fix will be released in the next couple weeks. In the mean time you can work around it by installing LibreOffice. You can do that by copying this into a Terminal window, pressing Enter, and waiting for it to complete:
flatpak install -y flathub org.libreoffice.LibreOffice
Then retry the OS update using the button in the Details pane of the Settings app.